Physical and mechanical characterization of Fiber-Reinforced Aerated Concrete (FRAC)

Fiber-Reinforced Aerated Concrete (FRAC) is a novel lightweight aerated concrete that includes internal reinforcement with short polymeric fibers. The autoclaving process is eliminated from the production of FRAC and curing is performed at room temperature. Several instrumented experiments were performed to characterize FRAC blocks for their physical and mechanical properties. This work includes the study of pore-structure at micro-scale and macro-scale; the variations of density and compressive strength within a block; compressive, flexural and tensile properties; impact resistance; and thermal conductivity. Furthermore, the effect of fiber content on the mechanical characteristics of FRAC was studied at three volume fractions and compared to plain Autoclaved Aerated Concrete (AAC). The instrumented experimental results for the highest fiber content FRAC indicated compressive strength of approximately 3 MPa, flexural strength of 0.56 MPa, flexural toughness of more than 25 N m, and thermal conductivity of 0.15 W/K m.     

Flexural toughness characteristics of steel–polypropylene hybrid fibre-reinforced oil palm shell concrete

Hybridization of steel–polypropylene leads to improvements of both the mechanical and ductility characteristics of concrete. In this investigation, the effect of steel, polypropylene (PP) and steel-PP hybrid fibres on the compressive strength, tensile strength, flexural toughness and ductility of oil palm shell fibre reinforced concrete (OPSFRC) was studied. The comparison on the above said properties between the specimens prepared with crushed and uncrushed oil palm shell (OPS) as lightweight coarse aggregate was also carried out. The experimental results showed that the highest compressive strength of about 50 MPa was produced by the mix with 0.9% steel and 0.1% PP hybrid fibres. The highest increments in the splitting tensile and the flexural strengths of the OPSFRC were found up to 83% and 34%, respectively. However, the mixes with 1% PP fibres produced negative effects on both the compressive and tensile strengths. The results on the toughness indices showed that the OPSC possess no post-cracking flexural toughness. Though, the flexural deflection and toughness of the OPSC was significantly enhanced by the addition of fibres; the dominance of the steel fibre on the first crack flexural deflection and toughness of OPSFRC was evident. The mixes with 0.9% steel and 0.1% PP hybrid fibres reported the highest improvement in toughness index and residual strength factor.     

Torsional behaviour of steel fibre-reinforced oil palm shell concrete beams

The increasing demand for curved structural members has prompted an increase in the research on the torsional behaviour of concrete. Recently, oil palm shell (OPS) has received considerable attention as a material that enables the production of sustainable lightweight concrete. This work investigated the effects of steel fibre of 0.25%, 0.50%, 0.75% and 1.00% volume fractions on the mechanical properties and torsional resistance of OPS concrete (OPSC) and OPS fibre-reinforced concrete (OPSFRC) beams. The experimental results showed that the increase in fibre content resulted in better mechanical properties and torsional resistance of OPSFRC. The compressive, splitting tensile and flexural strengths of OPSFRC with 1% steel fibres were found to be 40%, 110% and 150%, respectively, higher than the control mix. The crack bridging effect also improved the pre-cracking and post-cracking torsional behaviour of OPSFRC. The highest cracking torque, ultimate torque, twist at failure and torsional toughness of 8.3 kNm, 8.5 kNm and 1.31 kNm/m were obtained for the mix with 1% steel fibre. Moreover, the crack arrest ability of the steel fibre reduced the primary torsional crack widths and formed multiple fine cracks. Further, a simplified torsional model is proposed to predict the torsional behaviour of OPSC and OPSFRC.     

Lightweight geopolymer concrete containing aggregate from recycle lightweight block

In this research, the properties of lightweight geopolymer concrete containing aggregate from recycle lightweight block were studied. The recycle block was crushed and classified as fine, medium and coarse aggregates. The compressive strength and density with various liquid alkaline/ash ratios, sodium silicate/NaOH ratios, NaOH concentrations, aggregate/ash ratios and curing temperatures were tested. In addition, porosity, water absorption, and modulus of elasticity were determined. Results showed that the lightweight geopolymer blocks with satisfactory strength and density could be made. The 28-day compressive strength of 1.0–16.0 MPa, density of 860–1400 kg/m³, water absorption of 10–31% and porosity of 12–34%, and modulus of elasticity of 2.9–9.9 GPa were obtained. It can be used as lightweight geopolymer concrete for wall and partition.     

Effects of polypropylene twisted bundle fibers on the mechanical properties of high-strength oil palm shell lightweight concrete

In this study, the effects of a new type of non-metallic fiber (polypropylene twisted bundle (PPTB)) on the slump and mechanical properties of oil palm shell (OPS) concrete have been investigated. The results showed that increasing the volume fraction of PPTB fibers, it slightly decreases the workability and density of the concrete. It has found that the compressive strength of OPS concrete increases with increasing PPTB fiber volume fraction. The results revealed that the reinforcement of OPS concrete with steel and PPTB fibers reduces the strength loss of OPS concrete in poor curing environments. In addition, the fiber with low volume fraction (up to 0.25 %) is more efficient in improving the flexural strength of OPS concrete compared to its splitting tensile strength. The average modulus of elasticity (E value) is obtained to be 17.4 GPa for all mixes, which is higher than the values reported in previous studies and is within the range for normal weight concrete. The performance of the PPTB fibers is comparable to that for steel fibers at a volume fraction (V_f) of 0.5 %, which provides less dead load for lightweight concrete. The findings of this study showed that the PPTB fibers can be used as an alternative material to enhance the properties of OPS concrete. Hence, PPTB fibers are a promising alternative for lightweight concrete applications.     

Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

Mechanical performance of low cement reactive powder concrete (LCRPC)

The possibility of producing a reactive powder concrete (RPC) with low cement content was aimed in the scope of this study. Cement was replaced with class-C fly ash (FA) up to 60% for this purpose. Three different curing conditions (standard water curing, autoclave curing and steam curing) were applied to specimens. Two series of RPC composites were prepared with bauxite and granite aggregates. Mechanical properties such as compressive strength, splitting tensile strength, flexural strength and fracture energy of composites were investigated. Test results showed that, compressive strength of 200 MPa can be reached with low cement by using high-volume fly ash. Thermally treated specimens showed compressive strength beyond 250 MPa and high volume fly ash RPC have superior performance. Furthermore, compressive strength values reached up to 400 MPa with external pressure application during setting and hardening stages.     

Effects of heat treatment on oil palm shell coarse aggregates for high strength lightweight concrete

In this study, the effects of heat treatment on oil palm shell (OPS) coarse aggregates are evaluated for high strength lightweight concrete (HSLWC). OPS coarse aggregates are subjected to heat treatment at two temperature settings (60 and 150 °C) and duration of heat treatment (0.5 and 1 h). The reduction in density is found to be within the range of HSLWC when heat-treated OPS aggregates are added into the oil palm shell concrete (OPSC). The results reveal that workability of the OPSC increases with an increase in temperature and duration of heat treatment of the OPS aggregates. It is found that the maximum achievable 28-days and 90-days compressive strength is 49 and 52 MPa, respectively. Furthermore, the ultrasonic pulse velocity (UPV) is examined and the results showed that a good condition is achieved for the OPS HSLWC at the age of 3 days. The average modulus of elasticity (i.e. (E) value), is found to be 15.9 GPa for all mixes, which is higher than that reported in previous studies and is within the range of normal weight concrete. Hence, the findings of this study are of primary importance as they reveal that the selection of a suitable temperature and duration of heat treatment for OPS aggregates can be used as a new eco-friendly alternative method to enhance HSLWC.     

Assessment of factors influencing mechanical properties of steel fiber reinforced self-compacting concrete

In the last decade the steel fiber reinforced self-compacting concrete (SFRSCC) has been used in several partially and fully structural applications. This study investigates how the inclusion of steel fibers affects the properties of SFRSCC. For this purpose, an extensive experimental program including different cement contents of 400, 450 and 500 kg/m³, two maximum aggregate sizes of 10 and 20 mm along with steel fiber volume fractions of 0%, 0.38%, 0.64% and 1% was conducted. The water/cement ratio was kept constant at 0.45 for all the mixes studied. Mechanical properties were tested for compressive, splitting tensile and flexural strengths and modulus of elasticity. The results showed that mixture characteristics and volume fraction of steel fibers can significantly affect these major properties. Furthermore, this study represents extensive comparisons using database that have been gathered from a wide variety of international sources reported by many researchers and data obtained experimentally, which came up with about some discrepancies in the results.     

The role of 0–2 mm fine recycled concrete aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate concrete

The aim of this study is to investigate the role of 0–2 mm fine aggregate on the compressive and splitting tensile strengths of recycled concrete aggregate (RCA) concrete with normal and high strengths. Normal coarse and fine aggregates were substituted with the same grading of RCAs in two normal and high strength concrete mixtures. In addition, to keep the same slump value for all mixes, additional water or superplasticizer were used in the RCA concretes. The compressive and splitting tensile strengths were measured at 3, 7 and 28 days. Test results show that coarse and fine RCAs, which were achieved from a parent concrete with 30 MPa compressive strength, have about 11.5 and 3.5 times higher water absorption than normal coarse and fine aggregates, respectively. The density of RCAs was about 20% less than normal aggregates, and, hence, the density of RCA concrete was about 8–13.5% less than normal aggregate concrete. The use of RCA instead of normal aggregates reduced the compressive and splitting tensile strengths in both normal and high strength concrete. The reduction in the splitting tensile strength was more pronounced than for the compressive strength. However, both strengths could be improved by incorporating silica fume and/or normal fine aggregates of 0–2 mm size in the RCA concrete mixture. The positive effect of the contribution of normal sand of 0–2 mm in RCA concrete is more pronounced in the compressive strength of a normal strength concrete and in the splitting tensile strength of high strength concrete. In addition, some equation predictions of the splitting tensile strength from compressive strength are recommended for both normal and RCA concretes.     

Evaluating the effects of multi-walled carbon nanotubes on the mechanical properties of chopped strand mat/polyester composites

In this research, the influence of adding multi-walled carbon nanotubes at various contents on the mechanical properties of chopped strand mat/polyester composites was investigated. Initially, the effect of the sonication time on the dispersion of carbon nanotube at the highest weight ratio (0.5 wt.%) was inspected. To achieve this goal, a new technique based on scanning electron microscopy, which utilizes the burn-off test, was introduced to visualize the dispersion state of carbon nanotubes. Subsequently, the effect of addition of multi-walled carbon nanotube on the tensile and flexural properties of the fiber reinforced composites was studied. The results of mechanical tests showed that adding only 0.05 wt.% carbon nanotube enhanced the flexural strength of the hybrid composite by 45% while the tensile strength was not changed significantly. Improvements in the tensile and flexural moduli were also observed. Moreover, theoretical relations between the tensile, flexural and compressive moduli based on the classical beam theory were employed to determine the effect of carbon nanotube on the compressive modulus of composites. The theoretical result showed 31% enhancement in the compressive modulus.     

Flexural behavior of geopolymer composites reinforced with steel and polypropylene macro fibers

Like ordinary Portland cement concrete, the matrix brittleness in geopolymer composites can be reduced by introducing appropriate fiber reinforcement. Several studies on fiber reinforced geopolymer composites are available, however there is still a gap to understand and optimize their performance. This paper presents the flexural behavior of fly ash-based geopolymer composites reinforced with different types of macro steel and polypropylene fibers with higher aspect ratio. Three types (length-deformed, end-deformed and straight) of steel fibers and another type of length-deformed polypropylene fiber with optimum fiber volume fraction of 0.5% are studied. The effects of different geometries of the fibers, curing regimes (ambient cured and heat cured at 60 °C for 24 h) and concentration of NaOH activator (10 M and 12 M) on the first peak strength, modulus of rupture and toughness of the geopolymer composites are investigated. The quantitative effect of fiber geometry on geopolymer composite performance was also analyzed through a fiber deformation ratio. The compressive strength, splitting tensile strength and flexural toughness are significantly improved with macro fibers reinforcement and heat curing. The results also show that heat curing increases the first peak load of all fiber-reinforced geopolymers composites. End-deformed steel fibers exhibit the most ductile flexural response compared to other steel fibers in both heat and ambient-cured fiber reinforced geopolymer composites.     

Experimental investigation of the size effects of SiO2 nano-particles on the mechanical properties of binary blended concrete

In the current study, the size effects of SiO₂ nano-particles on compressive, flexural and tensile strength of binary blended concrete were investigated. SiO₂ nano-particles with two different sizes of 15 and 80 nm have been used as a partial cement replacement by 0.5, 1.0, 1.5 and 2.0 wt.%. It was concluded that concrete specimens containing SiO₂ particles with average diameter of 15 nm were harder than those containing 80 nm of SiO₂ particles at the initial days of curing. But this condition was altered at 90 days of curing. Also from the viewpoint of free energy, it can be concluded that the C–S–H gel formation around the particles with average diameter of 15 nm was more at the primary days of curing. This can be as a result of more nucleation sites that causes acceleration in early age strength. On the other hand, the growth probability of C–S–H gel around the 80 nm particles was more at 90 days of moist curing. This is due to the fact that the nucleus of strengthening gel could simply reach to the critical volume of nucleation that causes increase in the strength.     

Flexural performance of fiber-reinforced ultra lightweight cement composites with low fiber content

This paper presents an experimental study on flexural performance of ultra lightweight cement composites (ULCC) with 0.5 vol% fibers. Low density of the ULCC is achieved by using cenospheres from coal-fired power plants as micro aggregates. Effects of shrinkage reducing admixture (SRA) and fiber types on compressive strength and flexural performance of the ULCC are investigated. ULCC with density of 1474 kg/m³, compressive strengths of 68.2 MPa, flexural strength of 8 MPa, and deflection hardening behavior can be produced. Such good performance could be attributed primarily to the SRA which reduced entrapped air in paste matrix and densified fiber–matrix interface. The improvement on the flexural performance of the ULCC depends on fibers used and bond between fibers and matrix. Improvement of the flexural performance of the steel fiber (coated with brass) reinforced ULCC due to the densification effect by SRA was more significant than that of the PE fiber reinforced ULCC.     

Mechanical properties of reactive powder concrete containing high volumes of ground granulated blast furnace slag

The mechanical properties (flexural strength, compressive strength, toughness and fracture energy) of steel microfiber reinforced reactive powder concrete (RPC) were investigated under different curing conditions (standard, autoclave and steam curing). Portland cement was replaced with ground granulated blast furnace slag (GGBFS) at 20%, 40% and 60%. Sintered bauxite, granite and quartz were used as aggregates in different series. The compressive strength of high volume GGBFS RPC was over 250 MPa after autoclaving. When an external pressure was applied during setting and hardening stages, compressive strength reached up to 400 MPa. The amount of silica fume can be decreased with increasing amount of GGBFS. SEM micrographs revealed the tobermorite after autoclave curing.     

Experimental evaluation of fiber reinforced concrete fracture properties

Concrete is now universally recognized a construction material vital and essential for the regeneration and rehabilitation of the infrastructure of a country. The last few decades have now shown that high strength concrete, with a compressive strength of 100–120 MPa can be readily designed and manufactured. There have also been several advances made in the development of fiber reinforced concrete to control cracking and crack propagation in plain concrete, and to increase the overall ductility of the material. However, there are now many types of fibers with different material and geometric properties, and the exact fracture behavior of fiber reinforced concrete materials is not clearly understood. The overall aim of this paper is to establish the fracture properties and fracture behavior of concrete containing two widely used types of fibers, namely, steel (high modulus) and polypropylene (low modulus). The experimental investigation consisted of tests on cubes and notched prismatic specimens made from plain concrete and fiber concrete with 1% and 2% of steel or polypropylene fibers. The cube tests and the three point bending tests on notched specimens were carried out according to RILEM specifications, and extensive data on their compressive and flexural tensile behavior and fracture energy were recorded and analyzed. The results obtained from the tests are critically assessed, and it is shown that fibers contribute immensely to the structural integrity and structural stability of concrete elements and thereby improve their durable service life.     

Experimental study on the mechanical properties and microstructure of chopped basalt fibre reinforced concrete

With high ductility and sufficient durability, fibre reinforced concrete (FRC) is widely used. In this study, the effects of the volume fraction and length of basalt fibre (BF) on the mechanical properties of FRC were analyzed. Coupling with the scanning electron microscope (SEM) and mercury intrusion porosimeter (MIP), the microstructure of BF concrete was studied also. The results show that adding BF significantly improves the tensile strength, flexural strength and toughness index, whereas the compressive strength shows no obvious increase. Furthermore, the length of BF presents an influence on the mechanical properties. Compared with the plain concrete, the compressive, splitting tensile and flexural strength of concrete reinforced with 12 mm BF increase by −0.18–4.68%, 14.08–24.34% and 6.30–9.58% respectively. As the BF length increasing to 22 mm, corresponding strengths increase by 0.55–5.72%, 14.96–25.51% and 7.35–10.37%, separately. A good bond between the BF and the matrix interface is observed in the early age. However, this bond shows degradation to a certain extent at 28 days. Moreover, the MIP results indicate that the concrete containing BF presents higher porosity.     

Use of calcium carbide residue and bagasse ash mixtures as a new cementitious material in concrete

Calcium carbide residue (CCR) is a by-product of the acetylene gas production and bagasse ash (BA) is a by-product obtained from the burning of bagasse for electricity generation in the sugar industry. The mixture between CCR contains a high proportion of calcium hydroxide, while BA is a pozzolanic material, can produce a pozzolanic reaction, resulting in the products similar to those obtained from the cement hydration process. Thus, it is possible to use a mixture of CCR and BA as a cementitious material to substitute for Portland cement in concrete. The results indicated that concrete made with CCR and BA mixtures and containing 90 kg/m³ of Portland cement gave the compressive strength of 32.7 MPa at 28 days. These results suggested that the use of ground CCR and ground BA mixtures as a binder could reduce Portland cement consumption by up to 70% compared to conventional concrete that requires 300 kg/m³ of Portland cement to achieve the same compressive strength. In addition, the mechanical properties of the alternative concrete including compressive strength, splitting tensile strength, and elastic modulus were similar to that of conventional concrete.     

Influence of palm oil fuel ash on ultimate flexural and uniaxial tensile strength of green ultra-high performance fiber reinforced cementitious composites

This study focuses on the measurement of the ultimate flexural and tensile strength of GUSMRC, a new class of green ultra-high performance fiber reinforced cementitious composites (GUHPFRCCs) in which 75% of the volume contains ultrafine palm oil fuel ash (UPOFA). This green concrete is currently under development at the Universiti Sains Malaysia (GUSMRC). The main objective of this study is to investigate the potential of UPOFA as a partial binder replacement for the ultimate flexural and uniaxial tensile strength of GUSMRC mixtures. Results showed that UPOFA enhances the flexural and uniaxial tensile responses of fresh UHPFRCCs. The highest flexural and uniaxial tensile strength values at the 50% replacement level after 28 days were at 42.38 MPa and 13.35 MPa, respectively, indicating the potential of utilizing UPOFA as an efficient pozzolanic mineral admixture for the production of GUSMRC with superior engineering properties.     

Mechanical and morphological properties of fly ash/epoxy composites using conventional thermal and microwave curing methods

Conventional thermal and microwave curing methods were utilized to cure fly ash/epoxy composites, and the mechanical and morphological properties of the composites were evaluated. The conventional thermal curing was performed at 70 °C for 80 min while microwave curing was carried out at 240 W for 18 min in order to achieve the optimum cure of the composites, determined using Differential Scanning Calorimeter. The results suggested that the tensile and flexural moduli of the composites increased with increasing fly ash content while the effect became opposite for tensile, flexural and impact strengths, and tensile strain at break. Improved mechanical properties of the composite could be obtained by addition of N-2(aminoethyl)-3-aminopropyltrimethoxysilane coupling agent, the contents of 0.5 wt% being recommended for the optimum mechanical properties. Beyond these recommended contents, the mechanical properties greatly reduced, except for the flexural modulus. The comparative results indicated that the composites by the microwave cure consumed shorter cure time and had higher ultimate strengths (especially impact strength), and strain at break than those by the conventional thermal cure. The composites with higher tensile and flexural moduli could be obtained by the conventional thermal cure.