Tensile Behaviour of Slag-based Engineered Cementitious Composit

Engineered Cementitious Composites (ECC) have become another alternative in the concrete industry due to their excellent strain capacity under uniaxial tension. Research and development for new ECC mix incorporating wastes remain open to fulfil the industrial needs to produce green and sustainable ECCs. This paper presents the experimental work on the tensile and cracking behaviour of ECCs utilising industrial waste, namely ground granulated blast-furnace slag (GGBS), to replace cement. A total of four slag-based ECC mixes containing 2%–2.5% of PVA fibres and 50%-60% GGBS were investigated under uniaxial compressive and tensile tests. Compressive strength, tensile strength and the crack behaviours of the slag-based ECCs were evaluated and compared with a control mix. The experimental results show that the slag-based ECCs can achieve tensile strain capacity 2.6 %–2.75 % and ultimate tensile strength 1.43 MPa–2.82 MPa at 28 days. It was also found that the ECCs with GGBS and fibres formed few hairline cracks at the gage of the dog bone compared to brittle fracture in the control specimens.

Recent Advances in Strain-Hardening UHPC with Synthetic Fibers

This paper summarizes recent advances in strain-hardening ultra-high-performance concretes (UHPC) with synthetic fibers, with emphasis on their tensile properties. The composites described here usually contain about 2.0% high-density polyethylene (PE) fibers. Compared to UHPC with steel fibers, strain-hardening UHPC with synthetic fibers generally show a higher tensile ductility, lower modulus in the cracked state, and relatively lower compressive strength. The tensile strain capacity of strain-hardening UHPC with synthetic fibers increases with increasing tensile strength. The f’cftεt/w index (compressive strength × tensile strength × tensile strain capacity/tensile crack width) is used to compare the overall performance of strain-hardening UHPC. Moreover, a probabilistic approach is applied to model the crack width distributions of strain-hardening UHPC, and estimate the critical tensile strain in practical applications, given a specific crack width limit and cumulative probability. Recent development on strain-hardening UHPC with the use of seawater, sea-sand and PE fibers are also presented.

Effective Strain of BFRP for Confined Heat-Damaged Concrete Cylinders

It is widely accepted that concrete columns confined with fiber-reinforced polymer (FRP) jackets exhibit significant increases in strength and ductility with reference to the unconfined case. Existing experimental studies have indicated that the hoop rupture strains measured in the FRP jackets are significantly lower than the material strain capacity determined by the flat coupon tensile tests. An FRP efficiency factor is then usually used to define the ratio of the average hoop rupture strain to the material strain capacity of the FRP jackets, which governs the lateral FRP confinement as well as the peak strength and ultimate strain of the FRP-confined concrete under axial compression. FRP jackets are also expected to be a promising solution to repair damaged RC columns after fire exposure. However, there is lacking research on the behavior of FRP-confined fire or heat-damaged concrete columns. In particular, the FRP efficiency factor of FRP-confined fire or heat-damaged concrete columns has not yet been established. The study presents the results of an experimental study aimed to investigate the effects of the historical high temperature and the layer of basalt FRP (BFRP) jackets on the efficiency factor of BFRP for the confined heat-damaged concrete cylinders. A sum of 51 standard concrete cylinders is prepared and tested under axial compression. The parameters varied between tests are the historical high temperature (200°C, 400°C, 600°C, or 800°C) that is used to produce the heat damage of concrete cylinders and the number of layers of BFRP jackets (2, 3, or 4). The test results have indicated that the efficiency factor of BFRP jackets increases with the historical high temperature but decreases slightly with the increase in the BFRP layers. A new temperature-dependent design equation for the BFRP efficiency factor of the confined heat-damaged concrete is proposed to consider the effects of the parameters mentioned above and can be used for practical design.

Enhancing Strain Capacity by the Introduction of Pearlite in Bainite and Polygonal Ferrite Dual-Phase Pipeline Steel

In this study the strain capacity and work-hardening behavior of bainite (B), bainite + polygonal ferrite (B + PF), and bainite + polygonal ferrite + pearlite (B + PF + P) microstructures are compared. The work hardening exponent (n), instantaneous work hardening value (ni), and differential Crussard-Jaoul (DC-J) analysis were used to analyze the deformation behavior. The best comprehensive mechanical properties were obtained by the introduction of the pearlite phase in B + PF dualphase with the tensile strength of 586 MPa and total elongation of 31.0%. The additional pearlite phase adjusted the strain distribution, which increased the initial work hardening exponent and then maintained the entire plastic deformation at a high level, thus delayed necking. The introduction of pearlite reduced the risk of micro-void initiation combined with the high frequency of high angle grain boundaries (HAGBs) in triple-phase steel, which led to a low crack propagation rate.

Development of Engineered Cementitious Composites Using Sea Sand and Metakaolin

The present study investigates the possibility of using sea sand, instead of silica sand, in producing engineered cementitious composites (ECCs) and the optimal mix proportion, mechanical behavior, and erosive effect of chloride ions on sea sand ECCs (SECCs). Nine groups of SECC specimens were prepared based on the orthogonal test design, and these cured for the uniaxial tensile, uniaxial compression, and fracture energy tests. The roundness and sphericity of sea sand and silica sand were quantified by digital microscopy. The microstructure and composition of SECCs were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The mix proportions of SECCs with a tensile strain capacity more than 2% and a compressive strength more than 60 MPa were obtained. The factor analysis of these serial tests revealed that the contents of both fly ash and sea sand have a significant effect on the compressive strength and tensile strain capacity of SECCs. The fracture energy test revealed that the matrix fracture toughness of SECCs significantly increases with the increase in sea sand content. The XRD analysis revealed that the addition of metakaolin can enhance the ability of SECCs to bind chloride ions, and with the increase in chloride ion content, the ability of SECCs to bind chloride ions would improve. The results of the present study provide further evidence of the feasibility of using sea sand in the production of ECCs, in order to meet the requirements of diverse concrete components on ductility and durability.