Performance Of Polypropylene Fiber Reinforced Concrete Containing Slag

Polypropylene fibers have been introduced into concrete to overcome the weakness in tensile strength, improve the ductility and enhance the post elastic behavior and toughness. The industry waste Ground Granulated Blast Furnace Slag (GGBFS) was added to concrete as a cementitious material to replace part of cement to improve mechanical properties and make the polypropylene fiber reinforced concrete cheaper, which reduces the usage of cement and benefits environmental protection. Polycarboxylate acid-based superplasticizer is a new type of superplasticizer with outstanding water reducing properties. It improves the cement and superplasticizer compatibility significantly. Aiming at a number of theoretic and technical problems of plain concrete, high dispersion polypropylene fibers, GGBFS and polycarboxylate acid-based superplasticizer were introduced in concrete. The following contents are investigated basis on experimental testing and theoretical analysis: performance of fresh concrete, static mechanical properties, ultrasonic pulse velocity and flexural fatigue performance. The main conclusions are listed as follows:Polycarboxylate superplasticizer has good compatibility with polypropylene fibers and slag. The three materials significantly reduce slump loss of fresh concrete; polypropylene fibers prolong the invert slump cone time, increase air content, effectively inhibit the free shrinkage and reduce the density of concrete. Incorporation of slag also prolong the slump cone time, reduce the density and inhibit the free shrinkage of concrete, but has no significant effect on air content; polycarboxylate superplasticizer has significant influences on air content, free shrinkage and the saturated surface dry density.Results show that polypropylene fibers decrease the compressive strength and static elastic modulus but increase poission's ratio, while slag improves the compressive strength and static elastic modulus. The compatibility of acid polycarboxylate superplasticizer with cement presents good. The Composition effects of polypropylene fibers, slag and acid polycarboxylate superplasticizer are significant. A new constitutive formulation is proposed based on experimental data, which is more suitable to describe the relationship between static elastic modulus and compressive strength.Scanning electron microscope (SEM) testing reveal the hydrated products having different morphology which influences the compression properties. The study reveals that not only 0.1%～0.8%polypropylene fibers but also 35%～65% slag significantly enhance the tensile properties of concrete; moreover, the composite effects of 0.4% polypropylene fibers and 45% slag are most significant. SEM pictures reveal micro-structure mechanism of the reinforced effects. The splitting tensile strength of polypropylene fiber reinforced concrete containing slag ranged from 10% to 12% of its compressive strength. Based on this investigation, a 1.5075 power relationship between the splitting tensile strength and the compressive strength is derived for estimating the tensile strength of polypropylene fiber reinforced concrete containing slag.Polypropylene fibers are able to control the propagation of micro cracks and the development of macro cracks in concrete, and to improve concrete modulus of rupture. Fiber addition is seen to enhance the pre-peak as well as post-peak region of the load–deflection curve, causing an increase in energy absorbing capability. Slag particles can also benefit the density of concrete microstructure, thus improve flexural strength. The positive synergies of polypropylene fiber and slag are significantly both on physical and chemical aspects at the range from 0.1% to 0.6% volume fiber content with the range from 0 to 55% slag content. The highest flexural strength and toughness are obtained from the mixture of 0.4% polypropylene fiber and 55% slag. The highest residual strength factor is obtained from the mixture of 0.6% polypropylene fiber and 45% slag.The results indicate that flexural fatigue cumulative strength is more accurate to evaluate the concrete flexural fatigue performance; the incorporation of polypropylene fibers improves the flexural fatigue cumulative strength and fatigue life span; SEM examination show slag particles and its hydrated products benefit the density of concrete microstructure ,which improves ITZ structure and benefits flexural fatigue performance. A composite reinforce effect is found with the incorporation of slag and polypropylene fibers. The optimum mixture contents 55% slag with 0.6% polypropylene fiber for the cumulative fatigue stress. Fatigue properties are decreased as the stress level increasing; the S-N(Stress level-fatigue cyclic Number) models can be used to predict concrete life span. The higher frequency reduces the fatigue strength more than lower frequency at a constant stress level, the F-N (Frequency-fatigue cyclic Number) models can be used to predict concrete life span at different frequency.The experimental results present that the concrete compositions influence the ultrasonic pulse velocity significantly. Ultrasonic pulse velocity decreases by the increasing polypropylene fibers. The more slag incorporation, the larger ultrasonic pulse velocity is obtained. Changes of dosage of polycarboxylate superplasticizer have little influence on the pulse velocity for various W/Cs. The relative error of ultrasonic pulse velocity in polypropylene fibers reinforced concrete containing slag within±1% shows the reliability of the prediction model for concrete containing polypropylene fibers and slag. The prediction model is useful and relatively inexpensive nondestructive test (NDT)method in situ test for assuring the compressive strength of polypropylene fiber reinforced concrete containing slag placed in a structure.Research results present that the concrete containing above three materials as a new and higher performance price ratio building material has a broad applying prospect in hydraulic engineering and civil engineering.