Ran Huang

A method for testing the strength of concrete using uniaxial direct tension

Unlike steel, tensile strength in concrete is difficult to measure through direct testing because the brittleness of concrete will often produce local failure at both ends. This study presents a new method for testing the direct tensile strength of prismatic and cylindrical specimens. Concrete specimens with water/cement ratios of 0.45, 0.55, and 0.65 were designed and cast. Two #6 rebars were arranged along the longitudinal axis of specimens. The technique measured the direct tensile strength of the concrete by producing a uniform tensile stress along the length of the specimen, and, thus, minimized misalignment and stress concentration at both ends, which is predicted from finite element method analysis. This study found that the direct tensile testing method used here was a suitable method for estimating the tensile strength of concrete. The direct tensile strength of prismatic and cylindrical specimens with equal cross-sectional areas was similar. Although tensile strength is about 1/10 of compressive strength, the modulus of elasticity in tension and compression is about the same. Therefore, tensile and compressive strengths should show a statistically significant correlation.

Application on cementitious materials to promote durability of alkali-activated concrete containing co-fired fly ash and water-quenched slag

In the present study, we evaluated the effects of using co-fired fly ash (waste product of paper making) and water-quenched slag (waste product of iron smelting) in the manufacture of cementitious materials (CM). Rapid chloride permeability results revealed that less charge passes through CM than through ordinary Portland cement (OPC), indicating the superior durability of CM. However, the results of water permeability testing led to the opposite conclusion. Absorption capacity results revealed that the durability of CM is lower than that of OPC. Previous studies have shown that the strength of CM is only 70% that of OPC. This is a clear indication that CM containing co-fired fly ash and slag should not be used for primary structures, i.e., its use should be limited to secondary structures such as bricks or PC-based materials.Graphical abstract

Effect of Polyolefin Fiber on the Engineered Properties of Cement-Based Composites Containing Silica Fume

This study is aimed to evaluate the engineered properties of cement-based composites which comprise polyolefin fibers and silica fume in the mixes. Material variables include water-cementitious ratio, dosage of silica fume, polyolefin fiber length and dosage. Compressive strength, splitting tensile strength, direct tensile strength, resistivity, rapid chloride penetration test and microscopic observation were conducted. Test results indicate that the specimens containing silica fume have higher compressive strength than fiber and control specimens. The specimens with polyolefin fiber and silica fume have much higher tensile strength and ductility than the control and silica fume specimens. The specimens containing silica fume and polyolefin fiber demonstrate better resistance in chloride penetration than polyolefin fiber composites or silica fume composites. For a given volume fraction, short polyolefin fiber performs better than long polyolefin fiber in improving concrete properties. The specimen containing silica fume significantly increases in resistivity and decreases in total charge passed. SEM microscopy illustrates that the polyolefin fiber acts as the crack arresters in concrete, which can inhibit internal crack propagation.