| Polycarboxylate superplasticizers(PCE) is the most widely used water reducing agent,and more widely used in fiber reinforced concrete / mortar engineering and so on, so that produce the significant impact of construction performance, early strength as well as the durability of the fiber concrete / mortar. In this paper, the influnce mechanism of PCE on the fluidity and rheology of fiber cement paste was revealed, by studying the interface and adsorption behavior of PCE on the surface of fiber and cement particles, and provided the basic data and theoretical basis for the configuration and application of fiber concrete /mortar.In this paper, three kinds of ordinary fibers were used: polypropylene (PP) fiber,polyvinyl alcohol (PVA) fiber and sisal (JM) fiber, respectively, and the effects of fiber or fiber and PCE on the fluidity of cement paste were studied. The results showed that the three kinds of fibers had a negative effect on the fluidity of cement paste. With the increased of fiber length and dosage, because the fibers are easy to be intertwined and difficult to disperse, resulting the fluidity of cement paste was decreased. Due to the electrostatic repulsion, steric hindrance, hydration film and air-entraining lubrication of PCE, the initial fluidity of fiber and PCE cement paste is greatly improved, and the influence of fiber length and dosage on the fluidity of cement paste is consistent with the above. Compared with the three fibers, JM fiber had the greatest influence on the fluidity of the cement paste, and the PVA fiber was the second, and PP fiber had little effect.The effects of fiber and PCE on the apparent viscosity of cement paste were studied,and the shear stress-shear rate curves of cement paste were fit by Bingham and Herschel-Bulkley (H-B), reveal the yield stress and plastic viscosity and other rheological parameters with the fiber dosage and length of the law of change. The results show that with the increase of fiber dosage and length, the apparent viscosity and H-B plastic viscosity of cement paste increase gradually, and the influence of three kinds of fibers on viscosity is JM > PVA > PP. For the yield stress (H-B and Bingham), the data is basically 0,probably due to the less supportive force of fiber for cement particles, the bleeding in the between cement paste and the rotor, making the paste yield stress is zero.The adsorption amount of PCE on the surfaces of fiber and cement particle, and the synergistic adsorption amount of PCE on the surface of fiber and cement particle and the adsorption model were studied. Results showed that, the adsorption amount of PCE was the highest on the surface of JM fiber, and the PVA fiber was the second, and the PP fiber was the smallest. The synergistic adsorption capacity of PCE on the surfaces of the three kinds of fibers and cement particles was more than 0, indicating that added the fiber to cement pastes, and it was able to adsorption more PCE at the same time.The apparent roughness of the three fibers, and the contact angle of water and PCE on the fiber surface was studied. It is found that the surface of PP fiber and PVA fiber is smoother than JM fiber. The contact angle of water and PCE solution on PP fiber more than 90 °, which is hydrophobic fiber and the contact angle less than 90 ° on PVA and JM fiber, which is hydrophilic type fiber. Because of the JM fiber surface is more rough,and the contact angle is smaller than PVA fiber. The addition of fiber had a negative effect on the fluidity and rheological properties of cement paste, and the influence degree was JM >PVA > PP. Because the surface of JM fiber is rough, the contact area with cement and PCE increased,with the increase of fiber dosage and length,the synergistic adsorption capacity of PCE increases, resulting in the decrease of free PCE molecules in cement paste, and the impact of the subsequent fluidity and rheology of cement paste are increased. |
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