High Ductility Cementitious Composites Research Articles

High ductility cementitious composites incorporating seawater and coral sand (SCS-HDCC) for offshore engineering: Microstructure, mechanical performance and sustainability

In support of sustainable development strategies, engineering construction on remote islands is conductive to promoting the development of marine resources and mitigating increasingly severe resource conflicts. However, marine engineering, facing extreme weather and natural disasters, necessitates concrete with high ductility, durability and crack control capacity. This study evaluates the feasibility of using seawater and coral sand instead of fresh water and river sand to prepare the high ductility cementitious composites (SCS-HDCC). The results indicate that increased coral sand substitution introduces defects and expands the aggregate-matrix interfacial zone due to its rough surface, high specific area, and low strength. Coral sand's internal curing enhances compactness and reduces harmful pores. The dual action of seawater and coral sand, SCS-HDCC matrix is more tenacious, and the damage and blockage during the fiber pull-out process becomes obvious, and the slip hardening coefficient of fiber-matrix interfacial zone increases. SCS-HDCC achieves satisfactory ductility (up to 1.18 %) with initial cracking strength of 4.18 MPa, ultimate tensile strength of 5.66 MPa, and crack width of 71.2 ± 6.74 μm, average crack spacing of 6.02 mm. The SCS-HDCCs prepared in this study offers economic and environmental benefits by reducing economic costs and carbon emissions through transporting raw materials from the continent. The research results have guiding significance for the construction of islands and reefs by SCS-HDCC.

Synergistic effects of silica fume and slag on the microstructure and mechanical behaviors of ultra-high-strength and high-ductility cementitious composites

This work evaluated the synergistic effects of silica fume (SF) and ground granulated blast furnace slag (GGBS) binders on the microstructure and mechanical behavior of Ultra-High-Strength and High-Ductility Cementitious Composites (UHS-HDCC). The potential mechanisms of the synergistic effects of GGBS and SF on the fresh flow, mechanical properties, and microstructure of UHS-HDCC were investigated. The results indicated that the use of GGBS instead of SF could effectively improve the flowability of fresh mortar and UHS-HDCC mixtures. The hydration process of cement and the heat of hydration were delayed and reduced when the content of GGBS was below 25 %. Moreover, reducing the SF while increasing the GGBS reduced the compressive strength of the composites but had little effect on the flexural strength. The compressive strength of all specimens remained above 120 MPa. All specimens achieved strain-hardening behavior after the initial cracking of the matrix in uniaxial tension and four-point bending, and had a variety of cracking characteristics. Furthermore, the range of ultimate tensile strain capacity and mid-span deflection were 3.26 %–5.79 % and 16.73 mm–33.05 mm, respectively. The S10G30 specimen reached a maximum tensile strain energy of 414.6 kJ/m3. As the level of GGBS replacing SF increased, the number of cracks in the tensile region or the compressive bending surface of UHS-HDCC specimens increased, while the crack width and crack spacing decreased. The relatively smooth sidewalls of the fiber tunnels and fiber exit points meant that matrix fragments attached to the fiber surfaces were caused by matrix fragments generated throughout the matrix cracking process. Besides, the interfacial frictional stress and slip hardening coefficient acquired from the single fiber pullout test reduced with increasing levels of GGBS replacing SF.

Effect of PE fiber coated by polydopamine and nano-SiO2 on the strain hardening behavior of ultra-high-strength and high-ductility cementitious composites

Ultra-high molecular weight polyethylene (PE) fiber with startling mechanical properties and elastic modulus is considered an ideal reinforcing component for Ultra-High-Strength and High-Ductility Cementitious Composites (UHS-HDCCs). However, the fiber/matrix interfacial bonding is weakened due to the hydrophobic nature of the PE fiber surface, restricting the perfect expression of the PE fiber inherent characteristics. In this work, a promising technology for PE fiber surface functionalization using a combination of bio-inspired polydopamine (PDA) and deposited nano-SiO2 was proposed to enhance the fiber/matrix interfacial bonding in UHS-HDCCs. The results showed that PDA produced a uniform coating on the surface of PE fiber, and nano-SiO2 was successfully grafted to the surface of PE fiber through PDA coating as a bridge. The PDA and nano-SiO2 coatings introduced hydrophilic functional groups on the PE fiber surface, thereby enhancing the wettability of the PE fiber surface. The SiO2-PDA-PE fibers improved the ultimate tensile stress and tensile strain capacity of UHS-HDCCs to 117.1% and 130.2% respectively, compared to that of UHS-HDCCs incorporating pristine PE fiber. Furthermore, the SiO2-PDA-PE fibers effectively reduced the crack width and crack spacing while increasing the number of cracks and energy absorption capacity of UHS-HDCCs when subjected to increasing uniaxial tensile loading. The single fiber pullout results showed that both PDA-PE fibers and SiO2-PDA-PE fibers enhanced the peak force, chemical bond, frictional bonding stress, slip hardening coefficient, and pullout energy. Obviously, the positive effect of SiO2-PDA-PE fibers on the critical parameters of the fiber/matrix interface is higher than that of PDA-PE fibers except for the chemical bond. This work explored a novel way to modify the physicochemical performance of PE fiber surfaces for matching the strain hardening behavior of UHS-HDCCs, which is meant to guide the mix-design optimization of UHS-HDCCs.

Effects of Hybrid PVA–Steel Fibers on the Mechanical Performance of High-Ductility Cementitious Composites

Producing high-ductility cementitious composites (HDCC) increased in parallel with concrete demand in China recently. However, the high cost of manufacturing cementitious composites (HDCC) persists. To reduce the cost of HDCC, steel fibers, polyvinyl alcohol (PVA), and river sand were used to produce HDCC concrete in the present study. A total fiber content of 2% was formed with five different proportions of PVA fiber and steel fiber. Within the scope of the experimental studies, mechanical (workability, compressive strength, tensile, and bending properties), and microstructural (scanning electron microscopy) tests were carried out to investigate the properties of the hybrid fiber-reinforced composites. The results showed that the fluidity of HDCC increased with increasing steel fiber substitution. The compressive strength of the mixture containing 0.5% steel fiber and 1.5% PVA fiber exhibited a better compressive strength of 31.3 MPa. The tensile performance of the mixture was improved due to the incorporation of steel fiber. The initial cracking strength was about 2.32 MPa, 25.4% higher than that of the reference group, and the ultimate tensile strength was 3.36–3.56 MPa. However, reducing the content of PVA fiber impacts the flexural rigidity of the matrix.

Bond properties between concrete and high ductility cementitious composite with totally recycled fine aggregate

In order to explore the potential of high ductility cementitious composite with totally recycled fine aggregate (R-HDCC) as building repair material, the bond properties between concrete and R-HDCC were investigated through the double-face shear test in this study, which could be helpful for promoting the recycling of waste concrete, reducing environmental pollution and attaining better repair efficiency. The effects of concrete compressive strength, R-HDCC compressive strength and fiber volume fraction of R-HDCC on the bond properties between concrete and R-HDCC were analyzed in detail, and compared with those between concrete and high ductility cementitious composites with natural fine aggregate (N-HDCC). The acoustic emission technique was employed to monitor the internal damage of specimens, and the obtained signals were used as basis for analyzing the load bearing process. The experimental results showed that concrete/R-HDCC bonding specimen performed a higher bond strength and ductility than concrete/N-HDCC due to the tighter bond interface. The bond stress and slip at peak points on the bond stress-slip curve of concrete/R-HDCC specimens increased with the increasing of concrete compressive strength, R-HDCC compressive strength and fiber volume fraction of R-HDCC, while the bond stress at ultimate point decreased with the increasing of fiber volume fraction due to the larger slip and energy produced by more fibers pulled-out. Finally, the trilinear bond stress-slip model applicable to concrete/R-HDCC bonding specimen was established based on the statistical analysis of experimental results.

A Modified Fiber Bridging Model for High Ductility Cementitious Composites Based on Debonding-Slipping Rupture Analysis

Modified micromechanical bridging model is established with consideration of the fiber rupture effect at debonding and slipping stages. The bridging model includes the debonding and slipping rupture of fibers and establishes the fiber/matrix interfacial parameters (friction τ 0 , chemical bonding force G d , slip-hardening coefficient β ). A different interfacial bonding can cause fiber rupture. The influence of the interfacial conditions on the fiber rupture risk was investigated. In the modified bridging model, the effective bridging stress, the debonding rupture stress, and the slipping rupture stress were clearly identified. Finally, single-fiber pullout tests with different embedded lengths were carried out to validate the bridging model. The relationship between the fiber bridging stress and the crack opening predicted by the bridging model was consistent with the experimental results. This modified micromechanical bridging model can be used to quantitatively calculate the actual fiber bridging capacity and to predict the ductility of the high ductility cementitious composites reinforced by different types of fibers.

Design method of flexural capacity of BFRP bar reinforced ecological high ductility cementitious composites beam

Steel expansion joints are damaged under traffic loading, and bridge deck link slab made by basalt fiber reinforced polymer (BFRP) bar reinforced ecological high ductility cementitious composites (Eco-HDCC) can be used to replace the expansion joints. To provide the structural design guideline of bridge deck link slab, experimental study and theoretical analysis of BFRP bar reinforced Eco-HDCC bending beam were conducted. The diameter of BFRP bar and cover thickness were considered. Monotonic and cyclic loading modes were compared. When the diameter is within 8 mm ∼ 16 mm and the cover thickness is within 25 mm ∼ 35 mm, the peak load of beam increases as the diameter increases or the cover thickness decreases. Monotonic and cyclic loading regimes have little effects on the peak load. Before the beam cracks, diameter and cover thickness have little effects on the strain of BFRP bar and compressive strain of Eco-HDCC. After the beam cracks and under the same load, both the strain of BFRP bar and compressive strain of Eco-HDCC decrease as the diameter increases. Loading regime has little effect on the envelope curves of load-BFRP bar strain and load-Eco-HDCC compressive strain. Calculation formulas of flexural capacity for under-reinforced beam, balanced-reinforced beam and over-reinforced beam are established as the tensile stress–strain relationship of Eco-HDCC is involved. Compared with the test results, the calculation formulas of flexural capacity are feasible.

Property analysis and mixture design of high ductility cementitious composites with totally recycled fine aggregate based on target strength and strain capacity

The natural fine aggregate was completely substituted by the crushed waste concrete particles with original particle grade in preparing high ductility cementitious composite to promote the waste recycling, reduce the environmental pollution, realize the cleaner production and achieve the better properties in this study. The compressive and uniaxial tensile tests were conducted to analyze the effects of water-binder ratio, fiber volume fraction, recycled fine aggregate-binder ratio and fly ash content on the mechanical properties of high ductility cementitious composites with totally recycled fine aggregate (R-HDCC). The test results showed that the compressive strength of R-HDCC decreased significantly with the increasing of water-binder ratio. The peak tensile stress of R-HDCC was improved remarkably as fiber volume fraction increased and water-binder ratio decreased. The ultimate tensile strain of R-HDCC increased significantly with the increasing of water-binder ratio, fiber volume fraction and fly ash content, whereas reduced with the increasing of recycled fine aggregate-binder ratio. The relationships between the compressive strength, the peak tensile stress, ultimate tensile strain of R-HDCC and corresponding key parameters were set up according to the statistical analysis of test results. Then a mixture design method of R-HDCC based on the target strength and strain capacity was further developed. The detailed procedure of using the proposed mixture design method was illustrated with examples, and the reliability of the method was verified by the experimental results in this study and relevant literatures.

Mechanical and fiber/matrix interfacial behavior of ultra-high-strength and high-ductility cementitious composites incorporating waste glass powder

Most of the waste glass is landfilled, which is not conducive to the sustainability of the environment. However, waste glass powder (WGP) with sufficient fineness and high alkali reactivity exhibits excellent pozzolanic behavior, promoting its potential application in the concrete industry. This work evaluated the feasibility of replacing cement with WGP ranging from 0 to 30% to produce Ultra-High-Strength and High-Ductility Cementitious Composites (UHS-HDCC). The influences of WGP on the fresh flowability, mechanical properties, and fiber/matrix interfacial behavior of UHS-HDCC were investigated. The introduction of WGP enhanced the flowability of fresh UHS-HDCC mixtures. UHS-HDCC incorporating 10% WGP achieved incredible compressive strength, ultimate four-point bending stress, and ultimate uniaxial tensile stress, reaching around 158.4 MPa, 43.22 MPa, and 12.47 MPa, respectively. Moreover, all UHS-HDCCs exhibited strain-hardening features and multiple cracking behaviors. The maximum mid-span deflection and ultimate tensile strain capacity of UHS-HDCCs with WGP were distributed in 9.84 mm–13.83 mm and 5.88%–7.47%, respectively. Compared with WGP0, WGP10 and WGP20, the crack distribution in the WGP30 was more saturated and the number of narrow cracks was the largest. The results of the single-fiber pullout test indicated that the interface frictional bonding stress of WGP10 was reached 2.22 MPa, which represented a high ultimate four-point bending stress and ultimate uniaxial tensile stress. Furthermore, the average slip hardening coefficient of UHS-HDCCs ranged from 0.0032 to 0.0041. Based on the micromechanical model, the fiber ruptured fraction of WGP10 in the development of crack opening was calculated to reach 31.5%, which explained the decrease in maximum mid-span deflection and tensile strain capacity. Therefore, the experimental research will provide preliminary data for the scientific and efficient use of waste glass in engineering construction.

Effects of BFRP Bar Diameter and Cover Thickness on Fracture Behavior of BFRP Bar–Reinforced Ecological High-Ductility Cementitious Composites

Abstract To obtain the design parameters of bridge deck link slabs made of ecological high-ductility cementitious composite (Eco-HDCC) material reinforced with a basalt fiber-reinforced plastic (BFRP) by applying fracture mechanics concepts, the reinforcing effects of a BFRP bar on the fracture properties of BFRP bar–reinforced Eco-HDCC specimens were studied. First, cracking load, crack mouth opening displacement (CMOD), and deflection of specimens were monitored, and BFRP bar diameter and cover thickness were considered. The results indicate that both the diameter and cover thickness of BFRP bar have an obvious influence on the crack kinking angle. In addition, as the diameter of BFRP bar increases, the peak load, peak CMOD, peak deflection, and fracture energy of Eco-HDCC specimens increase, and these peak values of Eco-HDCC specimens after reloading also show the same trend. In addition, the peak load, peak CMOD, peak deflection, and fracture energy are larger if the Eco-HDCC specimen has a smaller cover thickness. However, the Eco-HDCC specimen with a BFRP bar cover thickness of 25 mm has a higher peak load after reloading than the specimen with a cover thickness of 15 mm when the bar diameters are 10 and 12 mm, respectively. In conclusion, BFRP bar diameters from 10 to 14 mm and a cover thickness of 25 mm are recommended when designing bridge deck link slabs.

Flexural properties of high ductility cementitious composites with totally recycled fine aggregate

The natural fine aggregate was totally replaced by recycled fine aggregate (RFA) containing crush dust to prepare recycled high ductility cementitious composites (R-HDCC) for making full use of waste concrete and obtaining better properties. A total of 45 slab specimens in 15 groups were manufactured to systematically investigate the effects of RFA particle size distribution, RFA-binder ratio (R/B), water-binder ratio (W/B), fiber volume fraction (Vf), fly ash content (FA/B) and fiber length (Lf) on the flexural properties of R-HDCC through the third-point test. The results showed that the specimens with the RFA containing crush dust and smaller particles performed best due to the denser matrix. The specimens with a moderate R/B of 0.4 had the highest peak flexural stress whereas the specimens with a smaller R/B of 0.2 had a higher ductility and energy absorption ability. The peak flexural stress and ductility decreased with the increase in W/B, but the fiber strengthen effect was greatest for specimen with a moderate W/B of 0.35. The peak flexural stress of specimen increased continuously as Vf increased from 0 to 2.0% whereas the ductility and energy absorption ability reached maximum when Vf increased to 1.5%. Small amount of fly ash could slightly improve the peak flexural stress of specimen while the achievement of higher ductility and energy absorption ability needed a higher FA/B. Finally, the prediction models of peak flexural stress and ductility ratio of R-HDCC were proposed, which showed good agreements with test results.

Flexural properties of PVA fiber reinforced high ductility cementitious composites containing calcium carbonate whisker

To reduce the cost and improve mechanical properties of PVA fiber reinforced high ductility cementitious composites (PVA-HDCCs), calcium carbonate (CaCO3) whisker (CW) was used to partially substitute PVA fibers, and thus a novel kind of the PVA-HDCC containing the CW was designed (PVA/CW-HDCC). Flexural properties of PVA/CW-HDCCs with the different PVA fiber and CaCO3 whisker contents were investigated. The results indicated that the PVA-HDCC flexural deflection hardening ability decreased with the PVA fiber content reduction. However, partially substituted PVA fibers by CWs improved the flexural strength, ultimate flexural deflection, flexural toughness and flexural deflection hardening behavior of PVA-HDCCs. Technique for Order Performance by Similarity to Ideal Solution (TOPSIS) analysis results indicated that the group with 1.5% PVA + 0.5% CW had a higher cost performance than that of the group with 2% PVA fiber. To further understand the flexural properties of the designed HDCCs, a semi-empirical mathematical model considering the influence of CaCO3 whisker was proposed for predicting the flexural strength and ultimate flexural deflection of PVA/CW-HDCCs. The theoretical calculation results showed that the proposed model can be employed to predict flexural properties of PVA/CW-HDCCs.

Corrosion behavior of steel bar embedded in high-ductility cementitious composites under the coupled action of dry–wet cycles and chloride attack

Purpose High-ductility cementitious composites (HDCC) have an excellent crack controlled capacity and corrosion resistance capacity, which has a promising application in structure engineering under harsh environment. The purpose of this study is to explore the corrosion mechanism of steel bar in HDCC. Design/methodology/approach Intact and the pre-cracked HDCC specimens under the coupled action of different dry–wet cycles and chloride attack were designed, and intact normal concrete (NC) was also considered for comparison. Corrosion behavior of a steel bar embedded in HDCC was analyzed by an electrochemical method, a chloride permeability test and X-ray computed tomography. Findings Steel corrosion probability is related to the chloride permeability of the HDCC cover, and the chloride permeability resistance of HDCC is better than that of NC. Besides, crack is the key factor affecting the corrosion of steel bars, and the HDCC with narrower cracks have a lower corrosion rate. Slight pitting occurs at the crack tips. In addition, the self-healing products and corrosion products fill up the cracks in HDCC, preventing the external aggressive ions from entering and thereby decreasing the steel corrosion rate. Originality/value HDCC has a superior corrosion resistance than that of NC, effects of variable crack width on corrosion behavior of steel bar in HDCC under the coupled actions of different dry–wet cycles and chloride attack are investigated, which can provide the guide for the design application of HDCC material in structure engineering exposed to marine environment.

Tensile Performance of High Ductility Cementitious Composites With Recycled Powder From C&D Waste

The effects of recycled powder (RP) on hydration, micro-structures, compressive strength and tensile properties of high-ductility cementitious composites (HDCC) were studied. Three mass ratios of RP ranging from 10, 30 to 60% were employed to partially replace the cement. The hydration kinetics of RP-amended matrix was measured to investigate the influence of RP on the cementitious hydration process and the phase development was quantified by the thermal gravimetric analysis. Mechanical properties, including the compressive and tensile properties of HDCCs were obtained at 28 days. The morphology of reinforced polyethylene fiber at the fracture surface was obtained by the environmental scanning electron microscope (SEM) analysis.

Influence of polyvinyl alcohol fiber and fly ash content on compressive creep properties of high ductility cementitious composites

The influence of polyvinyl alcohol (PVA) fiber volume fraction and fly ash content on the creep behavior of high ductility cementitious composites (HDCC) under compression was investigated. For this investigation, the creep behavior of four HDCC groups with cube compressive strength of 30–50 MPa, PVA fiber volume fraction of 1.5% and 2.0%, and fly ash content of 60% and 80% at 7 d and 28 d loading periods, respectively, were evaluated. A compressive creep model, which reflects the loading age and holding time, was established. The results revealed that when the load was applied at 7 d and 28 d, and then maintained for 245 d, the specific creep of HDCC ranged from 95×10-6/ MPa to 165×10-6/ MPa and from 59×10-6/ MPa to 135 × 10−6/ MPa, respectively. The corresponding creep coefficients ranged from 1.48 to 2.25 and from 1.10 to 1.94, respectively. The PVA fiber volume fraction and fly ash content were the main factors affecting the specific creep of HDCC, which increased with increasing fiber fraction and fly ash content. Under short-term loading, the fiber volume fraction played a leading role in the specific creep, and the fly ash content played the leading role during long-term loading. Furthermore, the specific creep and creep coefficient decreased significantly with increasing loading age. The classical creep model described by a power exponent function is suitable for HDCC.

Polyvinyl Alcohol Fiber Length Optimization for High Ductility Cementitious Composites with Different Compressive Strength Grades

The fiber length has a significant impact on the fiber bridging capacity and the mechanical properties of high ductility cementitious composites (HDCCs), which is related to fiber/matrix interfacial bonding. However, this fundamental knowledge of HDCCs design has rarely been investigated systematically. To this end, this study deeply investigates the effect of the fiber length on the bridging stress and the complementary energy with various fiber/matrix interfacial bonds in theory. Then, the mechanical performances of HDCCs with various fiber lengths and compressive strengths were evaluated experimentally. In micromechanical design, longer fibers can achieve stronger bridging stress and more sufficient complementary energy regardless of the fiber/matrix interfacial bonding properties. However, it should be noted that the increase in bridging capacity was quite slow for the overlong fibers and excessive interfacial bonding. The experiments indicated that overlong fibers (18 mm and 24 mm) easily twined on the mixer blade and were hard to disperse evenly. The HDCCs with shorter fibers displayed better workability. The compressive strength was less affected by the fiber length, and most striking differences were less than 5.0%, while the flexural properties and the tensile properties first increased and then decreased when the fiber length ranged from 6 mm to 24 mm. Consequently, the fibers with lengths of 9 mm and the fibers with lengths of 12 mm were better candidates for the HDCCs with compressive strengths of 30 MPa to 80 MPa, and fibers with lengths of 9 mm caused the HDCCs to exhibit higher ductility properties in general.

Fracture mechanics-based mixture optimization of ecological high-ductility cementitious composites modified with recycled asphalt concrete

To obtain a promising mixture of an Eco-HDCC (Ecological High-Ductility Cementitious Composites) modified with RAC (Recycled Asphalt Concrete) to cast bridge deck link slabs, the fracture behaviour of Eco-HDCCs with different levels of RAC replacement is examined. The CMOD (Crack Mouth Opening Displacement) as well as the deflection of Eco-HDCC are monitored, and two classical fracture mechanics models are compared. Results indicate that cracks in Eco-HDCC specimens are kinked, and RAC replacement level has little effect on the crack pattern. In addition, as the RAC replacement level increases, the peak load and second peak load of Eco-HDCC decrease, while the peak CMOD (or deflection) and second peak CMOD (or deflection) show the opposite trend. Moreover, to analyze the CMOD energy dissipation of Eco-HDCC, the curve area method seems to be better than the MTPM (Modified Two-Parameter Model) and the J-integral method. Larger RAC replacement level is helpful for the CMOD (or deflection) energy dissipation of Eco-HDCC. CMOD hardening energy is a dominant factor in the overall energy dissipation, and it increases with increasing RAC replacement level. Finally, the RAC replacement level of 100% is a promising choice to cast the bridge deck link slabs economically.

Bond Behaviors between Ribbed BFRP Bars and Ecological High Ductility Cementitious Composites

Direct pull-out method was conducted to explore the bond stress-slip response of ribbed basalt fiber reinforced polymer (BFRP) bars embedded in ecological high ductility cementitious composites (Eco-HDCCs). The effects of the embedment length and cover thickness on the bond properties between Eco-HDCCs and the bars were described. Results indicate that the failure characteristics of the specimens depend on the embedment length and cover thickness of the BFRP bars. As the embedment lengths of the bars increase, the ultimate bond stress decreases while the ultimate slip increases. Besides, both the ultimate bond stress and ultimate slip show an increasing trend if the specimen has a cover thickness of less than 45 mm, while the increasing trend is slower if the specimen has a cover thickness of more than 45 mm. In addition, the strain of the specimen surface depends on the cover thickness, and the strain increases when the cover thickness is in a range of15 mm–35 mm. Moreover, certain embedment lengths and cover thicknesses of the BFRP bars are recommended in the structural design of bridge deck link slabs. The bond stress-slip relationship models of the BFRP bars in Eco-HDCCs are proposed based on the test results.

Mechanical properties of high-ductility cementitious composites with methyl silicone oil

Methyl silicone oil is used to precondition silica sand for the preparation of high-ductility cementitious composites. Its effect on their mechanical properties is investigated. Results indicate that the presence of methyl silicone oil significantly enhances the ductility (tensile strain capacity) of high-ductility cementitious composites while undermining their compressive and flexural strengths. The strain hardening behaviour, which is indicated by the slope of the linearised tensile stress–strain curve following the first cracking point, was found to be a maximum at 2% methyl silicone oil followed by a gradual decrease at a higher methyl silicone oil content. This behaviour can be explained by the interaction mechanism of methyl silicone oil on the matrix and fibre–matrix interface. Methyl silicone oil is found to improve the fibre distribution as a result of the oil presence on the fibre surface. Microscopic observation reveals that the fibre–matrix interface becomes porous through the presence of thin rod-like hydration products. This reduces the fibre bonding to the matrix that facilitates pullout but increases the post-pullout friction, which is beneficial in ductility improvement.

Effect of incorporating reclaimed asphalt pavement on macroscopic and microstructural properties of high ductility cementitious composites

Reclaimed asphalt pavement (RAP) are fractional aggregates and particles from the demolition waste of old asphalt pavements. RAP is seldom used as aggregates in concrete due to old asphalt coated on the surface and its hydrophobic nature compared to natural aggregates, which may have an effect on reducing the workability and mechanical properties of hardened concrete significantly. This study investigated potential use of fine RAP to substitute river sand (RS) in the production of high ductility cementitious composites (HDCC), which is a unique high performance fiber reinforced cementitious composites with feature of higher tensile strain capacity. The results showed that it is viable to incorporate RAP as substitution in the production of HDCC, and HDCC containing RAP still had nearly constant compressive strength at 28 days. The ultimate direct tensile strain increased with the increase of RAP content significantly, and the maximum increase was about 70% when RS was 100% replaced by RAP. Further investigation revealed that RAP content modified matrix fracture toughness and fiber/matrix interface properties. The pseudo strain hardening (PSH) indices calculated from fiber bridging σ(δ) curves of HDCCs based on the micromechanical model explained the effect of RAP content on mechanical properties of HDCC.