Characterization of fiber-reinforced lightweight concrete made of stalite aggregates

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Characterization of fiber-reinforced lightweight concrete

made of stalite aggregates

Mémoire

Omar Metwally

Maîtrise en génie civil - avec mémoire

Maître ès sciences (M. Sc.)

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Résumé

Ce travail examine les propriétés mécaniques du béton léger (LWAC) fabriqué avec des granulats commercialement connus par Stalite et renforcé avec des fibres. Les paramètres étudiés comprenaient la résistance à la compression (25 et 40 MPa), le type de fibres (acier, synthétique, basalte-minibars ou BMB et hybrides) et la fraction volumique des fibres (0,5 et 1%). Les essais effectués comprenaient des essais de compression, de déformation axiale, de traction sous pression, de module d'élasticité, de flexion, de retrait et de perte de masse. De plus, des tests de pénétration des ions chlorure et de résistivité de surface ont été effectués pour examiner la durabilité du béton. Les résultats des essais ont montré que le coefficient d'efficacité du LWAC, défini comme le rapport entre la résistance à la compression et la densité, était supérieur de 16% à celui du béton de poids normal (NWC). De plus, le module d'élasticité de LWAC a chuté de 8,5 à 15,2% par rapport à celui de NWC alors que son coefficient de Poisson variait entre 0,2 et 0,24.

L'ajout de fibres a amélioré les propriétés mécaniques du LWAC. L'absorption d'énergie de LWAC a augmenté de 129% en augmentant la fraction volumique des fibres BMB de 0,5 à 1%. De plus, le module de rupture du LWAC était plus élevé que celui prévu avec les formulations ACI 318 (2014). Les résultats des tests de durabilité ont montré que la pénétration des ions chlorure de LWAC était « très faible » selon la classification ASTM C1202 (2012). De plus, l'utilisation d'agrégats légers a augmenté la résistivité de surface du béton jusqu'à 150%. Cependant, l'ajout de fibres d'acier a augmenté la pénétration des ions chlorure et diminué la résistivité de surface du mélange, tandis que l'ajout de fibres BMB n'a montré aucune influence sur les deux paramètres.

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Abstract

This study investigates the mechanical properties and durability of lightweight aggregate concrete (LWAC) made with expanded slate coarse aggregates (commercially-known as Stalite aggregates) and reinforced with different types of fibers. The parameters investigated included the compressive strength (25 and 40 MPa), the type of fibers (steel, synthetic, and basalt-minibars or BMB, and hybrid fibers), and the volume fraction of the fibers used (0.5 and 1%). The experimental tests conducted to characterize the obtained LWAC included compression tests, axial deformation tests, pressure tension tests, modulus of elasticity tests, flexure tests, shrinkage tests, and mass-loss tests. Furthermore, both chloride-ion penetration and surface resistivity tests were carried out to examine the durability of LWAC mixes. Test results showed that the efficiency ratio of LWAC, defined as the ratio of compressive strength to density, was 16% higher than that of normal weight concrete (NWC). Moreover, the modulus of elasticity of LWAC dropped by 8.5 to 15.2% compared to that of NWC whereas its Poisson’s ratio ranged between 0.2 and 0.24.

The addition of fibers significantly enhanced the mechanical properties of the LWAC. For instance, the energy absorption of LWAC increased by 129% by increasing the volume fraction of BMB fibers from 0.5 to 1%. Furthermore, the modulus of rupture of LWAC was higher than that predicted using ACI 318 (2014) formulations. In terms of durability, test results showed that the chloride penetration of LWAC was “very low” according to ASTM C1202 (2012) classification. Moreover, using lightweight aggregates increased the surface resistivity of concrete up to 150%. However, the addition of steel fibers increased the chloride penetration and decreased the surface resistivity of the mix while the addition of BMB fibers showed no influence on both parameters.

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1.1 Scope _______________________________________________________________ 4 1.2 Lightweight aggregates (LWA) __________________________________________ 4 1.3 Manufacturing of expanded LWA ________________________________________ 7 1.4 Previous studies on LWAC ______________________________________________ 7 1.5 Previous studies on fiber-reinforced light-weight concrete ____________________ 11 1.6 Durability of concrete _________________________________________________ 17 1.7 Outcome and objectives _______________________________________________ 18

Experimental program and methodology _____________________________ 20

2.1 Scope ______________________________________________________________ 20 2.2 Concrete mixes ______________________________________________________ 20 2.3 Aggregates _________________________________________________________ 22

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2.3.1 Lightweight aggregates __________________________________________ 22 2.3.2 Normal weight aggregates ________________________________________ 24 2.3.3 Fine aggregates _________________________________________________ 25 2.4 Cementitious materials ________________________________________________ 25 2.4.1 Cement _______________________________________________________ 25 2.4.2 Fly ash _______________________________________________________ 25 2.5 Admixtures _________________________________________________________ 26 2.6 Fibers______________________________________________________________ 26 2.7 Test matrix _________________________________________________________ 29 2.7.1 Compression tests _______________________________________________ 31 2.7.2 Compression tests with gauges _____________________________________ 32 2.7.3 Pressure tension tests ____________________________________________ 33 2.7.4 Determination of modulus of elasticity ______________________________ 35 2.7.5 Flexural tests __________________________________________________ 36 2.7.6 Shrinkage tests _________________________________________________ 39 2.7.7 Chloride ion penetration __________________________________________ 40 2.7.8 Surface resistivity _______________________________________________ 41 2.8 Mixing _____________________________________________________________ 42 2.9 Curing _____________________________________________________________ 43 2.10 Physical properties __________________________________________________ 44

Analysis and discussion __________________________________________ 46

3.1 Physical properties ___________________________________________________ 46 3.1.1 Light-weight aggregates __________________________________________ 46 3.1.2 Concrete ______________________________________________________ 48

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3.2 Mechanical properties _________________________________________________ 50 3.2.1 Compression tests _______________________________________________ 50 3.2.2 Pressure tension tests ____________________________________________ 63 3.2.3 Modulus of elasticity ____________________________________________ 64 3.2.4 Poisson’s ratio _________________________________________________ 68 3.2.5 Flexural test results ______________________________________________ 71 3.2.6 Shrinkage _____________________________________________________ 93 3.2.7 Mass-loss _____________________________________________________ 95 3.3 Durability __________________________________________________________ 96 3.3.1 Chloride penetration _____________________________________________ 96 3.3.2 Surface resistivity _______________________________________________ 99 3.3.3 Correlation between chloride ions penetration and surface resistivity ______ 102

Conclusions and recommendations _________________________________________ 104

1. Scope _____________________________________________________________ 104 2. Conclusions ________________________________________________________ 104

Tests on mechanical properties ___________________________________ 104 Durability tests _______________________________________________ 107

3. Recommendations for future work ______________________________________ 108

References ____________________________________________________________ 109

Appendix I ____________________________________________________________ 116

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List of figures

Figure 1-1: Development of compressive strength of Mix P (OPSC) and Mix L (expanded clay) at different ages (Shafigh et al., 2014)_____________________________________ 9

Figure 2-1: Samples of Stalite aggregates used in this study _______________________ 22

Figure 2-2: Dimensions and shape of BMB, steel, and synthetic fibers ______________ 27

Figure 2-3: Samples of the fibers used: (a) BMB, (b) synthetic, and (c) steel fibers _____ 27

Figure 2-4: a) Schematic of cylinders with 4 strain gauges installed (all dimensions in mm) and b) cylinder under compression ___________________________________________ 33

Figure 2-5: Bridgman's theory in PTT ________________________________________ 34

Figure 2-6: Pressure tension test setup: a) specimen C40 and b) air pressure control unit 35

Figure 2-7: Illustration of the composition of specimen C40-SB10 (all dimensions in mm) ______________________________________________________________________ 37

Figure 2-8: Flexural test setup ______________________________________________ 38

Figure 2-9: Schematic of the flexural test setup (all dimensions in mm) ______________ 38

Figure 2-10: Shrinkage mold _______________________________________________ 39

Figure 2-11: a) Rapid chloride penetration setup and b) Perma2 device ______________ 41

Figure 2-12: Surface resistivity test using Wenner method (extracted from Proceq Resipod

datasheet) ______________________________________________________________ 42

Figure 2-13: Mixing C40-S10 concrete mix____________________________________ 43

Figure 3-1: Average compressive strengths at 28 days for C25 mixes _______________ 51

Figure 3-2: Failure mode of cylinders cast with (a) C40 and (b) C40-B10 mixes _______ 52

Figure 3-3: Average compressive strength of the tested specimens __________________ 54

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Figure 3-5: Efficiency ratio using the equilibrium density_________________________ 59

Figure 3-6: Crack pattern of specimen C40-B10 at peak load ______________________ 60

Figure 3-7: Stress-strain relationships ________________________________________ 61

Figure 3-8: Energy absorption results ________________________________________ 63

Figure 3-9: Loading and unloading cycles on specimen C40-B10 __________________ 64

Figure 3-10: Average modulus of elasticity of the different mixes __________________ 65

Figure 3-11: Predicted versus experimental modulus of elasticity___________________ 67

Figure 3-12: Vertical stress versus lateral strains ________________________________ 69

Figure 3-13: Poisson’s ratio versus axial stress in compression tests ________________ 70

Figure 3-14: Crack pattern of C40-S05 after testing _____________________________ 72

Figure 3-15: Crack pattern of C40-S10 after testing _____________________________ 72

Figure 3-16: Crack pattern of C40-B05 after testing _____________________________ 73

Figure 3-17: Crack pattern of C40-B10 after testing _____________________________ 73

Figure 3-18: Crack pattern of C40-Y05 after testing _____________________________ 74

Figure 3-19: Crack pattern of C40-Y10 after testing _____________________________ 74

Figure 3-20: Crack pattern of C40-M10 after testing _____________________________ 75

Figure 3-21: Crack pattern of C40-SB10 after testing ____________________________ 75

Figure 3-22: Best-fit curves for C25 and C40 beams _____________________________ 79

Figure 3-23: Modulus of rupture, fp, energy absorption, T150, and equivalent flexural strength ratio, Rt 150, for C25 and C40 series __________________________________________ 80

Figure 3-24: Best-fit curves for beams C40-B05, C40-B10, C40-Y05, C40-Y10, C40-S05, and C40-S10 ____________________________________________________________ 85

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Figure 3-26: Modulus of rupture, fp, energy absorption, T150, and equivalent flexural strength ratio, Rt 150, of C40 specimens with 0.5% fibers _________________________________ 88

Figure 3-27: Load-deflection curves for B10, S10, Y10, SB10, and C40-M10 ___________________________________________________________________ 90

Figure 3-28: Modulus of rupture, fp, energy absorption, T150, and equivalent flexural strength ratio, Rt 150, of C40 specimens with 1% fibers __________________________________ 92

Figure 3-29: Shrinkage variation with time ____________________________________ 94

Figure 3-30: Mass change with time _________________________________________ 96

Figure 3-31: Rapid chloride penetration results _________________________________ 97

Figure 3-32: Surface resistivity results _______________________________________ 102

Figure 3-33: Correlation between chloride penetration and surface resistivity results __ 103

Figure A-1: Natural sand datasheet as provided by the manufacturer _______________ 116

Figure A-2: Normal weight coarse aggregates datasheet as provided by the manufacturer _____________________________________________________________________ 117

Figure A-3: Datasheet of cement type I as provided by the manufacturer ____________ 118

Figure A-4: Stress-strain relationships as obtained from compression tests for specimens (a) C40, (b) C40-B05, (c) C40-B10, (d) C40-S05, and (e) C40-S10 ___________________ 122

Figure A-5: Curve fitting for specimens C40 __________________________________ 123

Figure A-6: Curve fitting for specimens C40-B05 ______________________________ 123

Figure A-7: Curve fitting for specimens C40-B10 ______________________________ 124

Figure A-8: Curve fitting for specimens C40-S05 ______________________________ 124

Figure A-9: Curve fitting for specimens C40-S10 ______________________________ 125

Figure A-10: Curve fitting for specimens C40-Y05 _____________________________ 125

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Figure A-13: Curve fitting for specimens C40-SB10 ____________________________ 127

Figure A-14: Curve fitting for specimens C25 _________________________________ 127

Figure A-15: Curve fitting for specimens C25-B05 _____________________________ 128

Figure A-16: Curve fitting for specimens C25-B10 _____________________________ 128

Figure A-17: Integration of area under the load-deflection curve for C40 ___________ 129

Figure A-18: Integration of area under the load-deflection curve for C40-B05 _______ 129

Figure A-20: Integration of area under the load-deflection curve for C40-S05 ________ 130

Figure A-21: Integration of area under the load-deflection curve for C40-S10 ________ 131

Figure A-22: Integration of area under the load-deflection curve for C40-Y05 _______ 131

Figure A-23: Integration of area under the load-deflection curve for C40-Y10 _______ 132

Figure A-24: Integration of area under the load-deflection curve for C40-M10 _______ 132

Figure A-25: Integration of area under the load-deflection curve for C40-SB10 ______ 133

Figure A-26: Integration of area under the load-deflection curve for C25 ___________ 133

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List of tables

Table 2-1: Mix proportions of tested concrete in kg/m3 ___________________________ 21

Table 2-2: Physical properties of Stalite coarse aggregates (12.5 mm) _______________ 23

Table 2-3: Characteristics of Stalite aggregates (12.5 mm) ________________________ 24

Table 2-4: Test matrix* ____________________________________________________ 30

Table 3-1: Specific gravity and absorption of Stalite aggregates (Paul and Lopez, 2011) 47

Table 3-2: Oven-dry densities of concrete mixes ________________________________ 48

Table 3-3: Equilibrium densities of concrete mixes ______________________________ 49

Table 3-4: Compressive strengths at 28 days ___________________________________ 55

Table 3-5: Stress-strain relationships under axial compression _____________________ 61

Table 3-6: Fitting equation used for each mix __________________________________ 77

Table 3-7: Flexural test results ______________________________________________ 81

Table 3-8: Surface resistivity results ________________________________________ 101

Table A-1: Fly ash class F datasheet as provided by the manufacturer ______________ 119

Table A-2: Terms used in Fourier’s equation to best-fit flexure results _____________ 135

Table A-3: Terms used in Gaussian’s equation to best-fit flexure results ____________ 136

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Acknowledgment

I would like to express my deepest appreciation to my supervisor, Prof. Ahmed El Refai for his continuous guidance, encouragement, and patience. I would like to express my gratitude to Prof. Andrew Boyd and his team at McGill University for his support in conducting the surface resistivity and pressure tension tests. I wish to acknowledge all technical staff at Laval University especially Mr. René Malo and Mr. Pierre-André Tremblay for their continuous support. My gratitude is also extended to my colleagues in the Centre de

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Introduction

1. Background and problem statement

Concrete is classified according to its density to normal-weight concrete (NWC) with a density ranging between 2240 to 2480 kg/m3, and lightweight concrete with a density ranging between 1680 to 1920 kg/m3 (ACI 213, 2014). The use of lightweight concrete has been driven by the development in its technology and the emergence of artificial lightweight aggregates (LWA) and, more importantly, by the need for lighter concrete structures for economic and technical purposes.

Lightweight concrete has several advantages that make it a viable alternative to NWC in many structural applications. Besides its lightweight and, in some cases, its higher strength/weight ratio, lightweight concrete has higher impact and blast resistance than its normal weight counterpart, which makes it advantageous in several defense applications (ACI 213, 2014). It is also known for its high fire resistance due to its low thermal conductivity and low thermal expansion coefficient. In modern days, lightweight concrete becomes a crucial material in several construction applications such as in high rise buildings and seismic-resistant structures. The use of lightweight concrete in construction reduces the weight of the structure and therefore reduces the seismic design charges, which can lead to more economical structures.

On the other hand, lightweight concrete is known for its weakness and brittleness compared to NWC, which results in less energy absorption capacity and less shear, flexure and tensile strengths. Previous studies concluded that brittleness of lightweight concrete might lead to undesirable failure modes, which motivated many researchers to examine multiple solutions to overcome this drawback. Among these solutions are increasing the

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cement content. However, this approach compromises the concrete density and leads to denser concrete. Another approach is the addition of fibers in the concrete mixes aiming at improving the concrete tensile and flexure strengths and its toughness.

For decades, the most commonly added fibers to lightweight concrete mixes have been steel fibers that are cut in different shapes and different lengths. However, the use of steel fibers usually leads to an increased weight of the concrete mix due to their high density (about 7850 kg/m3), which is more than five times the density of lightweight concrete. To overcome such barrier, synthetic fibers have been used to enhance the mechanical properties of lightweight concrete. However, concrete mixes with added synthetic fibers showed inferior properties and long-term durability issues.

With the development in the fibers industry, new macro-fibers made of basalt fiber reinforced polymers (BFRP) and commercially known as basalt-minibars (BMB) have emerged as alternatives to conventional fibers. Despite the fact that a large number of studies investigated the mechanical properties of lightweight concrete in the last decades, a few numbers of studies have examined the effect of adding discrete fibers to lightweight concrete on its mechanical properties, not to mention the use of the newly-emerged BMB.

Therefore, this research aims at investigating the physical and mechanical properties of lightweight aggregate concrete (LWAC), made of expanded slate known commercially as (Stalite aggregates), and reinforced with BMB fibers. For the sake of comparison, other types of fibers were used in the tests namely, steel and polypropylene fibers. This combination of LWAC made with Stalite aggregates, and those types of fibers have never been examined or tested. Therefore, the objective of this study was to perform a primary investigation on the feasibility of improving the mechanical properties and durability of LWAC by the addition of different types and dosages of fibers to its mix.

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2. Thesis structure

The thesis is organized into five chapters as follows:

• Chapter (1) provides background on the subject and defines the research problem. • Chapter (2) provides a comprehensive review on previous research work that was

conducted on lightweight concrete and fiber-reinforced concrete among other relevant topics.

• Chapter (3) describes the tests executed and the methodology used to achieve the objectives of this study. It also provides an insight into the mechanical properties of the materials used in creating the lightweight concrete mixes. It also describes the procedure of preparing, mixing, and testing the specimens under study.

• Chapter (4) presents, analyzes, and discusses the test results and compares them with those found in the literature.

• Chapter (5) presents the conclusions of this research and recommendations for future work.

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Literature Review

1.1 Scope

In this chapter, previous studies that have been conducted to investigate the properties of lightweight aggregates (LWA), lightweight aggregate concrete (LWAC), fiber-reinforced concrete (FRC), and fiber-reinforced lightweight concrete are presented.

1.2 Lightweight aggregates (LWA)

Since aggregates occupy more than 70% of the concrete’s volume, their characteristics have an enormous effect on the concrete strength, durability, and structural performance. Aggregates were initially viewed as a filling material used for economic reasons. However, the physical, mechanical, and thermal properties of the aggregates used are vital factors in defining the mechanical properties of concrete. Moreover, the chemical properties of aggregates could define the concrete durability such as its resistance to sulfate attack and alkali-silica reaction. Aggregates are classified as fine and coarse aggregates according to their nominal maximum sieve size. They can also be classified according to their density to normal-weight and light-weight aggregates. Other classifications include their physical shape, manufacturing process, and aggregate source.

The use of LWA has been motivated by the desire to reduce the concrete weight and consequently reducing the cost of construction. Lightweight concrete is produced either by using lightweight aggregates, by eliminating a portion of the fine aggregates, or by creating air voids in the cement paste used. The latter method produces what is known as cellular concrete, which is created either by a chemical reaction that creates gas inside the cement

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idea behind eliminating fine aggregates to produce lightweight concrete is that fine aggregates have a smaller particle size with respect to coarse aggregates. Consequently, fine aggregates fill the void between coarse aggregates, which increases its density. Therefore, eliminating a portion of fine aggregates reduces the concrete density. The other approach to achieve lightweight concrete is by using lightweight aggregates in the concrete mix. This can be achieved by using either lightweight coarse aggregates or lightweight fine aggregates or both.

LWAs are found naturally such as the pumice, diatomite, and scoria aggregates whereas other LWA are manufactured such as the vermiculite, the perlite, and the expanded aggregates. Expanded LWA are made of clay, shale, fly ash, blast furnace slag, or slate. Despite the fact that natural LWA are in general lighter than the manufactured ones, their absorption is higher, and their strength is lower than the manufactured aggregates. With the limited resources of natural LWA and the environmental impact of extracting such aggregates, their use in producing lightweight concrete becomes limited (Neville, 2011).

LWA used in structural applications should satisfy the provisions of ACI 213 (2014) and ASTM C330/C330M (2014). For lightweight coarse aggregates, the dry loose bulk density should be less than 880 kg/m3_{, their shrinkage should not exceed 0.07%, and their} compressive strength should range between 17 and 28 MPa, depending on the equilibrium density of concrete. Moreover, ACI 213 (2014) described durable lightweight aggregates to have uniformly distributed pores with sizes ranging between 5 and 300 µm and relatively crack-free surface. The specific gravity of LWA should range from 1/3 to 2/3 of that of normal weight aggregates. Moreover, LWA has an absorption capacity between 25 and 75% of the apparent volume (Shink, 2003).

LWA enhanced the curing process of concrete by acting as an internal reservoir of water that enhanced the compressive strength of concrete (Paul and Lopez, 2011). However,

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this internal curing process is affected by the absorption percentage and the structure and size of pores. On the other hand, LWA is known for their durability problems due to their high permeability and high absorption of water, and consequently their inadequate resistance to chloride penetration. This deficiency is compensated by the use of high-strength mortars, which may overcome such drawbacks (Chandra and Berntsson, 2002-a).

Lightweight aggregate concrete (LWAC) can be produced using lightweight fine aggregates or lightweight coarse aggregates. The modulus of elasticity of LWAC made with expanded clay and sintered fly ash ranged between 17.8 and 25.9 GPa, which is much lower than NWC at compressive strengths between 50 and 90 MPa (Zhang and Gjørv, 1991 a). Cook (2007) proposed Equation 1 to calculate the modulus of elasticity for LWAC with oven-dry density, wc, that ranges from 1600 to 2480 kg/m3 and with compressive strength, fc’, ranging from 7 to 158 MPa:

𝐸𝑐 = 𝑤𝑐2.687 × (𝑓𝑐′)0.24 [1]

According to Neville (2011), Poisson’s ratio of LWAC varies between 0.15 and 0.25. ACI 213R-14 (2014) indicates that shrinkage of LWAC varies from 700 to 1100 µm for normally-cured specimens having a compressive strength of 40 MPa. On the other hand, according to ACI 318 (2014), the modulus of rupture of concrete is given by Equation 2 as follows:

𝑓𝑟 = 0.62𝜆√𝑓𝑐′ [2]

where λ equals:

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• 0.75 to 0.85 if lightweight and normal weight fine aggregates are mixed with lightweight coarse aggregates;

• 0.85 if normal weight fine aggregates are mixed with lightweight coarse aggregates; • 0.85 to 1 if normal weight fine aggregates are mixed with lightweight and normal weight

coarse aggregates.

1.3 Manufacturing of expanded LWA

Expanded LWA are produced in a rotary kiln by generating gases inside the raw material while heat is applied. Gases are then entrapped inside the material leading to a porous structure inside the aggregate after cooling, which eventually reduces the specific gravity of the aggregates as compared to the raw material. Expansion may also be achieved by the so-called sinter strand method, in which the moistened materials are burned gradually so that heat penetrates to its full depth evaporating the liquids from inside. Consequently, the gases entrapped in the material create a stable porous structure after cooling (Alexander and Mindess, 2005; Neville, 2011). The oven-dry specific gravity of expanded clay or shale LWA ranges from 1.2 to 1.5 for coarse aggregates and from 1.3 to 1.7 for fine aggregates. Their bulk density ranges from 350 to 900 kg/m3 for those made with sinter strand process and from 300 to 650 kg/m3 for those manufactured in a rotary kiln. Both aggregates can produce concrete with a density ranging from 1400 to 1800 kg/m3 (Neville, 2011).

1.4 Previous studies on LWAC

This section presents a brief literature review on previous research conducted on different types of lightweight aggregate concrete (LWAC).

Mo et al. (2015) compared between NWC and LWAC produced from oil palm shell (OPS) aggregates at three different compressive strengths (25, 35, and 45 MPa). Test results

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showed that the strength-to-density ratios (cube compressive strengths to saturated surface-dry densities) of OPS concrete (OPSC) were 0.0129, 0.0171, and 0.0218 MPa/kg/m3 compared to 0.0110, 0.0145, and 0.0166 MPa/kg/m3 for NWC of compressive strengths 25, 35, and 45 MPa, respectively. The results showed that the modulus of elasticity of OPSC was less than that of NWC while its dry shrinkage was 2.5 times higher after 150 days. Moreover, the bond strength of OPSC was 50 to 80% higher than that of NWC for the same compressive strength. The comparison between the performance of OPSC and expanded clay aggregates concrete showed that OPSC had 44% higher compressive strength and 30% and 16% higher flexural and splitting strengths, respectively. However, OPSC showed higher sensitivity to the curing time compared to the expanded clay concrete.

Calais (2013) investigated the mechanical properties, and durability characteristics of LWAC made with expanded shale aggregates. The author reported that the absorption of expanded shale concrete was time dependent. The 24-hour absorption was 9% compared to 20 and 30% after 50 days and more than one year, respectively. The author also reported that the modulus of elasticity of LWAC was 22.5 GPa whereas that of NWC was 34 GPa. The shrinkage value of LWAC after 50 days was 0.0003 mm/mm. The results of the shrinkage ring test (ASTM C1581, 2013) showed that stresses in LWAC were more than half of those in NWC. The author also reported that the high absorption capacity of aggregates jeopardized the concrete ability to resist freeze-and-thaw cycles by creating an internal pressure that led to the fracture of aggregates. This result was concluded after noticing several cracks on the prisms’ surface during freeze-and-thaw tests. The high porosity of the expanded shale aggregates and their weak modulus of elasticity were believed to be the reason for excessive axial deformations during the freeze-and-thaw tests. However, the axial deformations of most of the tested specimens were lower than 0.1%.

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those observed in tests conducted on OPSC showed a clear separation. The natural texture of OPS aggregates and their smooth surface weakened their bond to the cement paste. The authors reported that the efficiency factor (defined as the ratio of cylinder compressive strength to the air-dry density) for NWC of dry density of 2350 kg/m3 was 18,936 NM/kg compared to 22,128 and 17,025 NM/kg for OPSC and expanded clay concrete, respectively. As shown in Figure 1-1 the compressive strength of OPSC was sensitive to the curing age while that of the expanded clay concrete slightly varied after 28 days.

Figure 1-1: Development of compressive strength of Mix P (OPSC) and Mix L (expanded clay) at different ages (Shafigh et al., 2014)

Moravia et al. (2010) compared between the mechanical properties LWAC made of expanded clay coarse aggregates and NWC. The authors concluded that LWAC showed 22 to 28% less compressive strengths compared to NWC. The target compressive strengths were 20, 25, 30, and 40 MPa at 28 days of curing. LWAC mixes with target compressive strength of 40 MPa showed the lowest percentage of reduction in compressive strength compared to NWC with the same target strength. The compressive strength of NWC at 28 days was 44.9 MPa whereas that of LWAC was 33.2 MPa, which represented a reduction 26.1%. However, the compressive strength of LWAC showed an increase of 6 and 23% at 7 days and 28 days,

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respectively compared to the 3 days strength. NWC density increased by 0.9 and 2.7% for 7 and 28 days, respectively, compared to 1.67% and 1.92% for LWAC. Thus, the authors concluded that the efficiency factor of NWC increased with age, which decreased the difference between the efficiency factor of NWC and that of LWAC.

Paul and Lopez (2011) investigated the internal curing efficiency of LWA by studying the pores’ structure and the different factors that affected the internal curing and shrinkage. The authors reported that Stalite aggregates had an isolated closed porous structure. Furthermore, the absorption of Stalite aggregates decreased by the increase of aggregate nominal maximum size. The results showed that the uptake water of expanded slate aggregates was about 30 to 50% lower than that of the expanded clay aggregates. The authors suggested that the interconnectivity of pores was the reason that the uptake water increased by the decrease of the maximum aggregate size of the expanded slate aggregates. The authors concluded that the natural lightweight aggregates were better than artificial LWA in terms of internal curing performance. The results showed that expanded slate aggregates of 10 mm have 39.7% of capillary pores relative to the total porosity, which contributed to the internal curing process. Expanded clay aggregates of 5 mm have 60.5% of capillary pores. The use of expanded slate aggregates did not significantly affect the chloride ion penetration. However, the use of pre-wetted LWAs, in general, was able to reduce the autogenous shrinkage.

Youm et al. (2014) studied the effect of the type of aggregates on the mechanical properties of concrete such as compression, modulus of elasticity, and Poisson’s ratio. Among the aggregates used were Stalite aggregates of max size 13 mm. The specific gravity,

SG, of Stalite aggregates was determined as 1.44 at SSD condition (saturated surface-dry

condition) compared to 2.6 for crushed granite normal aggregate, 1.62 for Asanolite, 1.37 for Dols, 1.45 for Argex, and 1.21 for Liapor aggregates. Three compressive strengths were

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tomographic imaging showed that Stalite aggregates had the highest internal void space and the lowest sphericity. The authors stated that Stalite aggregates had randomly distributed and closed pores and lower absorption capacity compared to other aggregates. Concrete made of Stalite aggregates had a higher compressive strength value compared to other LWAC, which was attributed to the low sphericity of aggregates and their closed pores. It also showed the highest modulus compared to other LWAC mixes, but lower than that of NWC. The ratio between the compressive strength and modulus of elasticity of Stalite LWAC at 365 days was between 1.16 and 1.06 times of that of 28 days, respectively, which was higher than those measured for other LWAC mixes.

Real et al. (2015) examined the chloride penetration resistance of LWAC made of expanded clay aggregates (Leca and Argex), sintered fly ash aggregates (Lytag), and expanded slate aggregates (Stalite). The authors concluded that the aggregate type had little influence on the chloride penetration resistance of concrete. However, the resistance was exponentially affected by the w/c ratio used, which allegedly suggested that LWAC with less porous aggregates could have similar results as those of NWC. Similar results were observed in the compression tests conducted on the different mixes. Concrete made of Stalite aggregates had slightly different compressive strength than that of NWC. Consequently, the efficiency ratio (strength/density) of concrete made of Stalite aggregates was higher than that of NWC. The electric resistivity and chloride penetration showed no correlation with the aggregate type. Concrete made of Stalite and Leca aggregates appeared to perform similarly to NWC.

1.5 Previous studies on fiber-reinforced light-weight concrete

The primary function of fibers in concrete is to overcome its low tensile strength and low toughness and to increase its ductility. The physical properties and the dosage of fibers added to concrete are vital parameters that dictate their ability to enhance the mechanical

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properties of concrete (Zongjin, 2011). For shrinkage control, however, a small amount of fibers is generally sufficient to reduce or eliminate shrinkage cracks (Shah, 1990).

Domagała (2011) investigated the effect of adding steel fibers to LWAC made with fly ash aggregates known commercially as Pollytag. Three volume fractions of steel fibers were used: 0.4, 0.6, and 0.8%. The results showed that plain LWAC with w/c ratios of 0.37 and 0.55 had a dry shrinkage of 8 and 20% higher than NWC, respectively. The addition of steel fibers caused a reduction in shrinkage up to 25% compared to that of plain LWAC. The addition of steel fibers did not affect the compressive strength and the modulus of concrete, which was attributed to the low volume fraction of the fibers used. The addition of 0.8% of steel fibers increased the flexure strength by 49 and 61% at w/c ratios of 0.55 and 0.37, respectively.

Gao and Zou (2015) studied the effect of using hybrid fibers on the flexure strength and deformation capacity of LWAC. The hybrid fibers consisted of 13 mm long steel fibers and three different polyvinyl alcohol (PVA) microfibers with 6, 10, and 12 mm long. Results showed that the combination of 1% of PVA of 6 mm long and steel fibers resulted in the highest flexural strength, deformation capacity, and fracture energy compared to those obtained when either steel or PVA fibers were used separately.

Chen and Liu (2005) studied the effect of adding different fibers to LWAC made of expanded clay coarse aggregates of dry density 1.46 g/cm3 and maximum particle size of 15 mm. Three types of fibers were used namely, steel, carbon, and polypropylene (PP) fibers. The addition of 1% PP and steel fibers reduced the slump by 20.8 and 54.2%, respectively, compared to that of plain concrete. The results showed that the compressive strength increased by 10% with the addition of 1% of steel fibers. However, the addition of PP fibers reduced the compressive strength of the mix. The toughness index of concrete increased

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reached 1000 µ at age of 100 days. Adding a combination of carbon and steel fibers reduced the shrinkage by 30%.

Wang and Wang (2013) investigated the mechanical properties of LWAC reinforced with four different volume fractions of steel fibers (0.5, 1, 1.5 and 2%). The authors used high strength shale lightweight aggregates with a bulk density of 770 kg/m3. Test results showed an increase in the compressive strength of concrete with the increase in the volume fraction of steel fibers used (compressive strength of 60.4 and 74.8 MPa for steel fibers ratio of 0 and 2%, respectively). Test results also showed that the ultimate deflection increased with the increase of the steel fibers ratio. The authors also reported that the splitting tensile strength and impact resistance of concrete increased with the increase of the fibers ratio.

Lee et al. (2017) investigated the effect of compressive strength and the fibers ratio on the flexure behavior and energy absorption of steel fiber-reinforced concrete using steel fibers of 60 mm long. Test results showed that steel fibers did not affect the flexural performance of the specimens in the linear elastic stage and before the first peak load was achieved. However, the fibers dosage significantly increased the energy absorption of the tested specimens. Furthermore, the results showed that, at the post-cracking stage, the flexure strength increased with the increase of the fiber dosage. Beams reinforced with 0.375 and 0.5% fibers volume ratios exhibited a pronounced strain-hardening behavior. Increasing the concrete compressive strength from 25 to 35 MPa did not influence the post-cracking behavior but increased the first peak load. On the other hand, the authors reported that the energy absorption T150 (determined as the area under the load-deflection curve) depended mainly on the fiber volume ratio rather than the compressive strength of concrete. However, the equivalent flexural strength ratio (which is the ratio of energy absorption capacity to the first peak strength)depended on both the compressive strength and the fibers volume ratio.

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Choi et al. (2014) investigated the compression, flexural, shear strengths and toughness of fiber-reinforced LWAC made with artificial fine and coarse aggregates. Three types of fibers were used (steel, vinylon, and polyethylene fibers). Test results showed minor influence of the fiber types and dosage on the compressive strength of concrete. Furthermore, the polyethylene fibers had a negative effect on the compressive strength of concrete. The increase in splitting tensile strength in all fiber-reinforced mixes was more pronounced when using LWAC rather than NWC. The addition of fibers improved the flexural strength in both LWAC and NWC. The flexural strength of LWAC increased by 4 to 234% compared to an enhancement between 13 and 77% for NWC. The addition of fibers to LWAC changed the failure mode in shear tests to a more ductile failure mode. The fracture toughness of LWAC specimens increased by 556, 617, and 781%, when vinylon, steel, and polyethylene fibers were used, respectively.

Branston et al. (2016) investigated the mechanical properties of NWC concrete with two types of fibers: dispersed basalt fibers and basalt-minibars (BMB). Three dosages of BMB fibers were used: 6, 20, and 40 kg/m3 representing 0.3, 1, and 2% fiber volume ratios. A control mix having 40 kg/m3_{steel fibers (volume ratio of 0.51%) was also tested for} comparison. The authors reported that adding BMB fibers resulted in the loss of workability despite the using of high dosage of superplasticizer. The compressive strengths of concrete decreased from 37.9 to 20.9 MPa by the addition of 1% BMB fibers. The results showed that the flexural strength was not affected by the addition of the dispersed basalt fibers. Moreover, the failure of beams reinforced with dispersed basalt fibers was brittle compared to those reinforced with BMB fibers, which was attributed to the penetration of the cement hydration products between the individual basalt filaments of the fibers, as suggested from the images obtained by the scanning electron microscope (SEM). Beams reinforced with 1 and 2% BMB fibers experienced a strain-hardening behavior in their post-cracking stages. Furthermore, beams with BMB fibers were able to maintain 50 to 90% of the first peak load at a deflection

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fibers surface which could lead to the deterioration of fibers by time. After nine months, the SEM image showed an enormous reduction in the cement hydration products around the fibers compared to those observed after 7 days. This result suggested the presence of a deterioration mechanism due to a chemical reaction between the fibers and the cement products. Thus, the authors suggested avoiding the use of high alkaline cement and the addition of pozzolanic filler to the ordinary Portland cement when BMB fibers are used.

Libre et al. (2011) investigated the feasibility of improving the ductility of pumice LWAC by the addition of hybrid fibers (a blend of steel and polypropylene fibers). The authors reported a reduction in the workability of all mixes. The authors suggested that workability is evaluated using the inverted slump test. Test results showed that steel fibers significantly decreased the workability of concrete compared to polypropylene fibers. Slump test results showed that adding 0.4% of polypropylene fibers resulted in an increase in the discharging time from 22 to 67 s. Moreover, the addition of 0.5% steel fibers increased the discharging time to 120 s. On the other hand, the addition of 0.5% steel fibers increased the compressive strength by 47%. Nevertheless, no further improvement in compressive strength was observed by increasing the fibers ratio. The addition of 0.5% steel fibers increased the toughness from 5.5×10-2_{to 19.8×10}-2_{. Increasing the ratio to 1% increased the toughness} from 26.6 ×10-2 MPa. The addition of 1% of steel fibers also increased the flexural strength by 150%. The results also showed no effect of polypropylene fibers on the compressive strength of concrete. However, adding 0.4% of polypropylene fibers by volume resulted in doubling the toughness of the mix.

Jiang et al. (2014) investigated the effect of adding discrete basalt fibers and polypropylene fibers on the mechanical properties of NWC. The authors reported a decrease in workability and an increase in the compressive, tensile, and flexural strengths by adding both types of fibers. The increase in strengths depended on the length of the fibers used. However, the authors observed a decrease in the compressive and flexural strengths after 90

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days. The results also showed that the flexure strength decreased by the increase of basalt fibers ratio from 0.3 to 0.5%. The authors observed debonding of the basalt fibers after 90 days, which explained the reduction in strengths. The SEM image at 7 and 28 days showed that the interfacial bond between the cement paste and the fibers was lost after 28 days. The results also showed an increase in the voids of concrete with fibers after 28 days. The authors recommended the use of 0.3% basalt fibers ratio as an optimum ratio.

Kayali et al. (1999) studied the effect of polypropylene and steel fibers on the dry shrinkage behavior of high-strength LWAC made with sintered fly ash aggregates. The authors replaced 23% of cement content by fly ash. The results of shrinkage measurements

showed that dry shrinkage of NWC was stabilized at 500 µ after 400 days while that of plain

LWAC increased up to 1060 µ after 790 days. Moreover, the addition of polypropylene fibers did not significantly reduce the dry shrinkage of the mixes while steel fibers slightly reduced it by 7.5 % at 500 days when 1.7 and 1.13% of steel fibers were used.

Güneyisi et al. (2014) investigated the effect of adding steel fibers on dry shrinkage, and mass-loss of LWAC made with cold-bonded fly ash lightweight coarse aggregates. The

results showed that shrinkage and mass-loss of plain LWAC was 790 µ and 172 g, respectively, after 50 days. The addition of steel fibers reduced dry shrinkage and mass-loss by 8 and 5%, respectively. Moreover, increasing the percentage of the added fibers did not result in any further reduction in shrinkage. The authors reported similar shrinkage and mass-loss results for mixes with 0.25, 0.75, and 1.25 % steel fibers.

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1.6 Durability of concrete

The durability of concrete is considered as a vital aspect when new materials are used. Some studies suggested that the use of fibers in concrete increased its vulnerability to long-term deterioration and chemical attack (Branston et al. 2016) while other studies reported that the presence of fibers decreased the concrete permeability (when no stress was applied) and hence enhanced its long-term performance (Banthia and Bhargava, 2007).

Banthia and Bhargava (2007) reported that increasing the stress applied to the concrete specimen to a certain threshold led to a decrease in its permeability as the applied stress closed the concrete pores and suggested that this threshold was 0.3fu, where fu is the compressive strength of concrete. However, this threshold increased to 0.5fu in fiber-reinforced concrete regardless of the fiber volume used.

Thomas (2006) investigated the chloride permeability of LWAC made of expanded slate with maximum aggregates size 5 and 10 mm for fine and coarse aggregates, respectively. The results of rapid chloride tests showed that the electrical charges that passed through NWC and LWAC specimens were 644 and 621 Coulombs (C), indicating almost similar behavior between both mixes.

Zhang and Gjorv (1991) b investigated the water and chloride ion permeability of ultrahigh-performance LWAC made of expanded clay aggregates. The electrical charge that passed through LWAC with w/c ratio of 0.28 and compressive strength of 102.4 MPa was 233 C in the chloride penetration test. Moreover, the electrical charge that passed in specimens with 0.36 w/c ratio and compressive strength of 84.5 MPa was 930.9 C.

Kim et al. (2015) investigated the durability of fiber-reinforced NWC made of steel, polypropylene, and polyvinyl alcohol fibers by immersing the specimens in acetic acid. Test

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results showed an increase in the concrete resistance to permeability, absorption, and chlorine ion diffusion by the addition of polyvinyl alcohol fibers and steel fibers. However, no significant change was observed when polypropylene fibers were added. The authors reported that the residual strength of concrete decreased dramatically after the exposition of the fiber-reinforced concrete to an acidic environment.

Zadeh and Bobko (2014) investigated the mechanical characteristics of LWAC using Stalite aggregates after being exposed to elevated temperature. Test results revealed that there was less degradation in the mechanical properties of LWAC exposed to elevated temperature compared to NWC.

1.7 Outcome and objectives

The following conclusions were drawn from the conducted literature review:

• Most of the previous studies have focused on determining the mechanical properties of LWAC. It has been well established that most of the produced LWAC had less mechanical properties compared to their NWC counterparts.

• The effect of fibers on the mechanical properties of LWAC is still controversial, and it is mainly dependent on the type of aggregates, the w/c ratio used, and the type, dosage, and the aspect ratio of the added fibers.

• Very few studies investigated the effect of adding fibers on the durability of LWAC not to mention when the newly-emerged basalt-minibars (BMB) were used.

• While a few studies investigated the mechanical properties of LWAC made with the expanded slate aggregates commercially known by Stalite (Paul and Lopez 2011; Real et al. 2015; Youm et al. 2014; Zadeh and Bobko 2014), no previous studies have addressed the effect of adding fibers on the mechanical properties of this type of LWAC.

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• No previous studies were conducted to examine the effect of adding the BMB fibers on the mechanical properties and durability of LWAC.

Therefore, the current study aims at filling some of these gaps that were found in the literature to understand better the behavior of LWAC mixes. The study focused on examining the mechanical properties and durability of LWAC made with Stalite aggregates and reinforced with different types and dosages of fibers with a focus on the BMB fibers. Based on the outcome of the conducted literature review, the research objectives have been set as follows:

• To investigate the feasibility of improving the mechanical properties of LWAC made with Stalite coarse aggregates by the addition of different types and dosages of fibers to its mix (BMB, steel, and synthetic fibers).

• To examine and determine the mechanical properties and durability of LWAC made with Stalite aggregates.

• To examine the mechanical properties and durability of fiber-reinforced LWAC made with Stalite aggregates and reinforced with different types of fibers.

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Experimental program and methodology

2.1 Scope

This chapter presents the experimental program and the methodology that has been adopted in preparing and testing the specimens. The chapter gives an insight into the types of specimens, types of tests conducted, tests’ setup, measurement techniques, among others. The chapter starts by presenting the properties of the materials used as detailed in the following sections.

2.2 Concrete mixes

Two mixes of concrete were used in this study namely the C25 and C40 mixes with target compressive strengths of 25 and 40 MPa at 28 days, respectively. The constituents of all mixes are shown in Table 2-1. Mixes were labeled according to their compressive strength (25 or 40 MPa) followed by the type of the fibers added, if any (S for steel, B for basalt-minibars or BMB, Y for polypropylene, SB for layered specimens, and M for mixed fibers). The last digits in the mix label indicate the volume fraction of the fibers added (0.5 or 1%). For instance, C40-B10 is a concrete mix that has a compressive strength of 40 MPa with 1% of BMB fibers added. The mix labels were also used to describe the tested specimens cast with the mix.

As will be explained later in this chapter, some specimens were not cast but extracted from a concrete slab after being hardened (core specimens). These specimens were given the letter ‘E’ at the end of their label (such as the extracted specimen C40-B10-E). In addition, control specimens made of normal weight concrete (NWC) were given the letter ‘N’ at the

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Table 2-1: Mix proportions of tested concrete in kg/m3

Specimen Cement Fly ash Water Stalite aggregates Crushed stones Fine aggregates w/c ratio Fibers BMB Steel Synthetic Lightweight C25 mixes (f’c = 25 MPa)

C25

320 0 176 612 - 770 0.55

- - -

C25-B05 10 -

-C25-B10 20 -

-Lightweight C40 mixes (f’c = 40 MPa) C40 410 50 190 568 - 680 0.41 - - - C40-B05 10 - -C40-B10 20 - -C40-S05 - 39.2 - C40-S10 - 78.5 - C40-Y05 - - 4.6 C40-Y10 - - 9.2 C40-M10 10 39.2 -

Normal weight C40-N mix (f’c = 40 MPa)

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2.3 Aggregates

2.3.1 Lightweight aggregates

Expanded slate coarse aggregates commercially known as Stalite aggregates were used in this study to produce lightweight aggregate concrete (LWAC) mixes. Stalite aggregates have angular and irregular shape with rough surface texture as shown in Figure 2-1. Stalite mines are located in North Carolina in the United States of America.

Figure 2-1: Samples of Stalite aggregates used in this study

The nominal maximum size of Stalite aggregates used is 12.5 mm. According to the manufacturer’s datasheet, Stalite aggregates are made of expanded slate that is formed from volcanic ash. The raw material is heated to high temperature ranging between 1000 and 1200o C in a rotary kiln. The physical properties and sieve analysis of Stalite aggregates are shown in Table 2-2 as reported in the manufacturer's datasheet.

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Table 2-2: Physical properties of Stalite coarse aggregates (12.5 mm)

Density Kg/m3

Dry Loose (ASTM C 29) 800

Dry Rodded (ASTM C 29) 896

Saturated Surface Dry Loose (ASTM C 29) 832

Damp Loose (ASTM C 29) 800-864

Specific gravity, SG Kg/m3

Dry SG (ASTM C 127) 1.47

Saturated Surface Dry SG (ASTM C 127) 1.53

Range in Saturated Surface Dry SG (ASTM C 127) 1.49-1.55

Sieve Size % passing

1" (25 mm) 100 3/4" (19 mm) 100 1/2" (12.5 mm) 90-100 3/8" (9.5 mm) 40-80 #4 (4.75 mm) 0-20 #8 (2.36 mm) 0-10 #16 (1.18 mm) 0 #30 (600um) 0 #50 (300um) 0 #100 (150um) 0

Table 2-3 shows the soundness, toughness, stability, impurities content, electrical resistance, and chemical characteristics of Stalite aggregates as tested by the manufacturer. As reported in their datasheet, these properties give the aggregates an excellent interlock connection with the concrete paste, resulting in better load transfer and higher compressive strength of concrete.

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Table 2-3: Characteristics of Stalite aggregates (12.5 mm)

Soundness (% Loss)

Magnesium Sulfate (ASTM C 88) 0 - 0.01%

Sodium Sulfate (ASTM C 88) 0 - 0.23%

25 Freeze-and-Thaw Cycles (AASHTO T 103) 0.22 - 0.80%

Toughness

Los Angeles Abrasion (AASHTO T 96) 25 - 28%

Stability

The angle of Internal Friction (Loose) 40° - 42° The angle of Internal Friction (Compacted) 43° - 46°

Impurities

Clay Lumps (ASTM C 142) 0

Organic Impurities (ASTM C 40) 0

Pop outs (ASTM C 151) 0

Electrical Resistance

Lab (AASHTO T 288) 30,000 - 40,000 ohm-cm

Field (ASTM G 57) > 500,000 ohm-cm

Aggregate Chemical Characteristics

Ignition Loss (ASTM C 114) 0

Stains (ASTM C 641) None

Sulfur Trioxide <0.05 ppm

Chlorides (NaCl) 0.60 - 7.0 ppm

Soluble Salts 0.28 mmhos/cm

pH 7 - 9

2.3.2 Normal weight aggregates

The normal weight aggregates (NWA) were used mainly in control specimens for comparison purpose. They were made from crushed stones with the nominal maximum size of 14 mm. The sieve analysis data of NWA are shown in Appendix I. The NWA were obtained from a local manufacturer in Québec city. They had an SG of 2.672 and absorption of 0.59%.

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2.3.3 Fine aggregates

The fine aggregates used in this study were natural sand obtained locally in Québec city. The sieve analysis data for fine aggregates used are given in Appendix I. The nominal maximum size of fine aggregates was 5 mm. The specific gravity saturated surface dry (SSD) condition was 2.7 with absorption of 0.5%, according to the manufacturer datasheet.

2.4 Cementitious materials

2.4.1 Cement

Ordinary Portland cement type I was used in preparing all the tested specimens. The cement has an initial setting time of 115 min and a compressive strength of 37.8 MPa at 28 days according to the manufacturer datasheet shown in Appendix I. The water used in the mix was normal tap water with a water/cement ratio, w/c, of 0.41.

2.4.2 Fly ash

Fly ash Class F acquired locally from Ciment Québec was used to partially replace the cement content in the mixes as a pozzolanic material. The use of fly ash was suggested to reduce the weight of the concrete mix and to improve its properties by forming less permeable concrete that is not vulnerable to chemical attacks (Manmohan and Mehta, 1981). During concrete curing, the fly ash reacts with the calcium hydroxide (CaOH2), which results from the cement hydration process, to produce the calcium silicate hydrate (C-S-H), which is characterized by a dense, small, and crystal shapes that fill the voids in the mix. This reaction decreases the permeability, enhances the chloride penetration resistance, and increases the long-term compressive strength of the mix (ACI 232.2R, 2003). Fly ash class F also

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contributes to the chemical reaction and the hydration of the cement (Chandra and Berntsson, 2002b). It is important to note that studying the effect of fly ash on concrete is not among the objectives of this study. The properties of fly ash used in this study are given in Appendix I.

2.5 Admixtures

High-range water reducer known commercially as EUCON 37 was used in this study. The admixture used complies with ASTM C494 provisions for admixtures type A and type F. As per the manufacturer’s datasheet, the recommended amount of the admixture is 400 to 1170 ml per 100 kg of cementitious material. An amount of 560 to 920 mL was used depending on the type of the desired mix.

2.6 Fibers

Three different type of fibers were used in this study namely, macrofibers made of basalt fiber-reinforced polymers (BFRP) and commercially known as basalt-minibars or BMB, hook-end steel fibers, and fibers synthetic made of polypropylene and polyethylene blend. Figure 2-2 and Figure 2-3 shows the shape and dimensions of the three types of fibers used.

It is important to note that the basalt fibers used in this study are different from the widely known as chopped basalt fibers, which were reported in many previous studies such as in Branston et al. (2016); Jiang et al. (2014). It was reported that chopped basalt fibers reduced the workability of concrete and caused durability concerns to the concrete mix such bond deterioration between the fibers and concrete. They also increased the percentage of voids in the mix, which resulted in a considerable decline in the mechanical properties of the mix. On the other hand, details about the BMB fibers are given in the following section.

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Figure 2-2: Dimensions and shape of BMB, steel, and synthetic fibers

Figure 2-3: Samples of the fibers used: (a) BMB, (b) synthetic, and (c) steel fibers

Basalt-minibars (BMB) fibers

Basalt-minibars (BMB) fibers are made of basalt fiber-reinforced polymer (BFRP) bars with a diameter of 0.5 mm and length of 43 mm ±1 mm giving an aspect ratio of 86 according to the manufacturer’s datasheet. BMB fibers are shown in Figure 2-2 (a). BMB fibers are coated with Vinylester and have a helical shape and a rough surface to increase the bond

S tee l S y nthetic B MB S y nthetic S tee l B MB

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between the fibers and concrete. The fibers have a specific gravity SG = 2, which is close to that of concrete (2.5 to 3.5) revealing good workability while mixing. According to the manufacturer’s datasheet, BMB fibers are characterized by a high tensile strength (1080 MPa) and a modulus of elasticity of 43 GPa, resembling the longitudinal BFRP bars and exceeding the properties of commonly-used chopped basalt fibers.

A few investigations have reported on the use of BMB fibers in concrete. According to Adhikari (2013), the addition of 0.5% by volume of BMB fibers to concrete resulted in increases of 15% in the concrete shear strength and 13% in its flexural strength. The addition of 0.75% BMB fibers increased the flexural strength of concrete by 25 to 55%. Adhikari (2013) also reported an increase of 11.5% in the concrete modulus due to the addition of 0.5% BMB fibers compared to the ACI-318 (2014) specified value for the same compressive strength. Adhikari (2013) reported that BMB fibers could be mixed to a ratio up to 4% by volume with NWC without affecting the workability of the mix. The author suggested Equation 3 and Equation 4 to predict the flexural strength of concrete having BMB fibers as a function of the fibers dosage as follows:

𝑓_𝑟 = (0.62 + 0.2 𝑉_𝐹0.45)√𝑓′_𝑐 ≤ 0.82√𝑓′_𝑐 with 27.5MPa ≤ 𝑓′_𝑐 ≤ 48MPa [3] 𝑓𝑟 = (0.62 + 0.3 𝑉𝐹0.45)√𝑓′𝑐 ≤ 0.92√𝑓′𝑐 with 48MPa ≤ 𝑓′𝑐 ≤ 62MPa [4]

where VF is the fiber ratio by volume varying between 0 and 1.5% and 𝑓′𝑐 is the specified compressive strength.

Steel fibers

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were cold-drawn with a low carbon content, which complies with ASTM C1116 and ASTM A820 standards. Steel fibers are shown in Figure 2-2 (b). According to the manufacturer, the fibers had a tensile strength of 1100 MPa. The dosage suggested by the manufacturer ranged between 15 and 60 kg/m3 of concrete. Two percentages of volume of steel fibers namely 0.5 and 1% were used in this study.

Synthetic fibers

A blend of polypropylene-polyethylene macro-synthetic fibers was used in this study. The specific gravity of fibers was 0.92, which was lower than that of steel and BMB fibers. Synthetic fibers had a modulus of 9.5 GPa with a tensile strength of 600-650 MPa. The fiber length was 51 mm with an aspect ratio of 74 according to the manufacturer’s datasheet. The dosage recommended by the manufacturer ranges from 1.8 to 12 kg/m3, which was equivalent to about 0.2% to 1.3% ratio by volume. Two percentages of volume of synthetic fibers namely 0.5 and 1% were used in this study.

2.7 Test matrix

In this study, different tests were accomplished to evaluate the main properties of lightweight aggregate concrete (LWAC) mixes made of Stalite aggregates. Table 2-4 shows the test matrix of the experimental program along with the number and type of the tested specimens. The experimental program adopted to determine the mechanical properties of concrete included the following tests:

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Table 2-4: Test matrix*

Concrete density Compression tests,

days Compression

with gauges

Pressure tension

Modulus of

elasticity, days Flexural tests

Oven-dry Equilibrium 3 7 28 7 28

C40 specimens: Control

C40 3 3 3 3 6 3 3 1 3 3

C40-N 3 3 3 3 3 - - - - -

C40 specimens: with 0.5% fibers

C40-B05 - - 3 3 3 3 - 1 3 3

C40-S05 - - - - 3 3 - - - 3

C40-Y05 - - - - 3 - - - - 3

C40 specimens: with 1% fibers

C40-B10 3 3 3 3 6 3 3 2 4 3 C40-S10 - - - - 4 3 3 - - 3 C40-Y10 - - - - 3 - 3 - - 3 C40-M10 - - - - 3 - 3 - - 3 C40-SB10 - - - 3 C40-B10-E - - - - 3 - - - - - C40-S10-E - - - - 4 - - - - - C25 specimens C25 - - - - 4 - - 2 2 3 C25-B05 - - - - 4 - - 2 2 3 C25-B10 - - - - 4 - - 2 2 3

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Shrinkage and mass-loss Chloride penetration Surface resistivity C40 specimens: Control

C40 4 7 3

C40-N - - -

C40 specimens: with 0.5% fibers

C40-B05 - 4 -

C40-S05 - 3 -

C40-Y05 - - -

C40 specimens: with 1% fibers

C40-B10 3 2 3 C40-S10 2 3 3 C40-Y10 - - 3 C40-M10 - 2 3 C40-SB10 - - - C40-B10-E - - - C40-S10-E - - - C25 specimens C25 - - - C25-B05 - - - C25-B10 - - -

*_{Note: The numbers shown refer to the number of specimens tested}

2.7.1 Compression tests

Compression tests were conducted according to ASTM C39 (2016) provisions. Standard cylinders of diameter 101 ± 2 mm and length of 202 ± 4 mm were tested under axial compression load to determine the compressive strengths of different concrete mixes after 3, 7, and 28 days of curing in the moist room. Table 2-4 shows the number of cylinders tested for each mix. All cylinders were pre-surfaced prior to testing to avoid any misalignment during load application. As listed in Table 2-4, compression tests were conducted on specimens made of C25, C40, and C40-N series.

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In order to study the influence of the casting method and the specimen’s dimensions on the compressive strength of concrete, compressive tests were also conducted on “extracted or core specimens.” For this purpose, two concrete slabs of 250×350×250 mm were cast using C40-B10 and C40-S10 mixes as given in Table 2-4. The slabs were cast in three equal layers of concrete. Each layer was compacted 100 times using a metal rod of 16 mm diameter. The slab surface was then finished with a metal trowel and covered with wet burlap for 24 hours. The slabs were then placed in the moist room for 24 hours before de-molding. Standard cylinders of 101×202 mm were then extracted from the slabs using a fixed diamond core drilling machine.

2.7.2 Compression tests with gauges

Compression tests were conducted on three standard cylinders of diameter 101 ± 2 mm and length of 202 ± 4 mm as per the test matrix is given in Table 2-4. During these tests, one cylinder was equipped with 4 strain gauges of 60 mm length attached vertically and horizontally on its side as shown in Figure 2-4. The other two cylinders were equipped with two vertical strain gauges only. The gauges used had a gauge factor of 2.13 ± 1% and resistance of 119.9 ± 0.5 Ω, with temperature compensation of 11 × 10-6_{/ºC and transverse} sensitivity of 0.8%. As listed in Table 2-4, compression tests were conducted on C40, C40-B05, C40-B10, C40-S05, and C40-S10 specimens.

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Figure 2-4: a) Schematic of cylinders with 4 strain gauges installed (all dimensions in mm) and b) cylinder under compression

The Poisson’s ratios of different concrete mixes were determined as the quotient of the vertical strain to the horizontal strain obtained during the tests. One cylinder was used to determine the Poisson’s ratio for each mix. The average of each pair of horizontal and vertical gauges was used in the calculations. Poisson’s ratios were determined as follows:

µ𝑝 =

𝜀_{𝑣𝑒𝑟𝑡𝑖𝑐𝑎𝑙} 𝜀ℎ𝑜𝑟𝑖𝑧𝑜𝑛𝑡𝑎𝑙

[5]

2.7.3 Pressure tension tests

Pressure tension test (PTT) is an alternative test to the conventional splitting test, which is usually used to determine the tensile strength of concrete. PTT is based on Bridgman’s theory as illustrated in Figure 2-5. In PTT, uniform tensile stresses are created across the entire cross-section and through the tested length of the cylinder. The circumference pressure

Characterization of fiber-reinforced lightweight concrete made of stalite aggregates