Conventional cement composite is generally produced with ordinary Portland cement (OPC) as a binder. However, during manufacturing the cement composite, large amount of carbon dioxide (CO2) are emitted. Therefore, fly ash is proposed to be replaced to OPC in order to reduce CO2 emission of cement composites. For reinforcing fibers, micro steel fibers were used. For investigating mechanical properties of steel fiber-reinforced cement composites (SFRCCs), direct tension tests were conducted. The test results showed that fly ash improves tensile strength and ductility of SFRCCs. However, tensile strength of the SFRCC decreased as replacement ratio of recycled fine aggregate increased. The use of recycled materials in FRCC helps to save natural resources and promote sustainability in civil engineering materials.
This research investigates the interfacial behavior between polyethylene (PE) fiber-reinforced strain-hardening cement composite (PE-SHCC) and reinforcing bars that are spliced in the tension region to determine feasibility of reduced lap-spliced length in PE-SHCC. Twenty test specimens were subjected to monotonic and cyclic tension loads. The variables include the replacement levels of an expansive admixture (0% and 10%), the compressive strength of the SHCC mixtures (40 MPa and 80 MPa), and the lap-spliced length in the tension region (40% and 60% of the splice length recommended by ACI 318). The PE-SHCC mixture contains polyethylene fiber to enhance the tensile strength, control the widths of the cracks, and increase the bond strength of the lap splice reinforcement and the calcium sulfo-aluminate- (CSA-) based expansive admixture to improve the tension-related performance in the lap splice zone. The results have led to the conclusion that SHCC mixtures can be used effectively to reduce the development length of lap splice reinforcement up to 60% of the splice length that is recommended by ACI 318. The addition of the calcium sulfo-aluminate-based expansive admixture in the SHCC mixtures improved the initial performance and mitigated the cracking behavior in the lap splice region.
This research examines the influence of an embedded steel reinforcing bar and micro steel fibers on the tensile and electrical properties of polyethylene (PE) fibers reinforced cement composite dumbbell-shaped specimens with multi-walled carbon nanotubes (MWCNTs) in direct tension. The cement composites are reinforced with 0.75 vol.% PE fibers to achieve a strain-hardening performance in direct tension and 1.0 wt % MWCNTs are incorporated to give the electrical conductivity into the cement composites. To investigate the steel bar and steel fibers effect on the electrical behavior of synthetic PE fiber reinforced strain-hardening cement composites (PE-SHCCs), a round bar with a diameter of 4 or 7 mm is placed at the center of specimen’s cross-section. Additionally, steel fibers’ content of 0, 0.5 and 1.0 vol.% are added into the PE-SHCC mixtures. The test result indicates that the addition of steel fibers improves the tensile strength and electrical behavior of synthetic PE fiber reinforced SHCC. The self-sensing ability of PE-SHCC with 1.0% steel fibers is improved by the presence of the embedded steel bar before an initial crack while the reinforced PE-SHCC specimens were less sensitive as the tensile strain increased after the initial crack. The optimal linear regressions between fractional changes in resistivity (FCR) and tensile strain were achieved for PE-SHCC containing 1.0% steel fibers.
This work evaluated the applicability of polyethylene (PE) fiber reinforced strain-hardening cement composite (PE-SHCC) layer at the bottom of reinforced concrete (RC) beams to improve the flexural performance and cracking behavior. PE-SHCC material with specific compressive strength of 70MPa was reinforced with 1.5% PE fibers at the volume fraction. Four RC beams with cross-section of 130 x 170mm and length of 1,460mm were made and tested under four-point monotonic loading. Three beams were layered with PE-SHCC material and one whole RC beam was a control specimen for comparison. Principal variable is the thickness of PE-SHCC layer; 20, 40 and 60mm that are equivalent to 11, 23 and 35% of beams depth. Experimental results indicated that the addition of PE-SHCC layer enhanced the crack-damage mitigation of RC beams and improve the structural behavior, such as strength and ductility, of RC beams.
This paper presents the influence of silica sand, local crushed sand and different supplementary cementing materials (SCMs) to Portland cement (C) ratio (SCM/C) on the flexural fatigue performance of engineered cementitious composites (ECCs). ECC is a micromechanically-based designed high-performance polymer fiber reinforced concrete with high ductility which exhibits strain-hardening and micro-cracking behavior in tension and flexure. The relative high cost remains an obstacle for wider commercial use of ECC. The replacement of cement by SCMs, and the use of local sand aggregates can lower cost and enhance greenness of the ECC. The main variables of this study were: type and size of aggregates (local crushed or standard silica sand), type of SCMs (fly ash “FA” or slag), SCM/cement ratio of 1.2 or 2.2, three fatigue stress levels and number of fatigue cycles up to 1 million. The study showed that ECC mixtures produced with crushed sand (with high volume of fly ash and slag) exhibited strain hardening behavior (under static loading) with deformation capacities comparable with those made with silica sand. Class F-fly ash combined with crushed sand was the best choice (compared to class CI fly ash and slag) in order to enhance the ECC ductility with slag–ECC mixtures producing lowest deflection capacity. FA–ECC mixtures with silica sand developed more damage under fatigue loading due to higher deflection evolution than FA–ECC mixtures with crushed sand.
Strain hardening behavior of lightweight hybrid polyvinyl alcohol (PVA) fiber reinforced cement composites