Papers by Author: You Jun Xie

Abstract: In order to understand microstructure characteristics and properties of reactive powder cementitious materials with low w/b, the A.C impedance test on reactive powder cementitious materials is carried out. The correlation between the impedance parameters, microstructure and properties of reactive powder cementitious materials is also analyzed. Results indicate that the impedance-frequency curve both for reactive powder mortar and ordinary cement mortar consists of vertical part in range of low frequency section and horizontal part within high frequency section. But the angle between vertical part and horizontal part of curve for reactive powder mortar is larger compared with ordinary specimen. There is a good linear relationship between the real part of impedance and angular frequency ω-1/2 for mortar when frequency is from 10Hz to 100Hz. And the slope φ of line increases with the additions of reactive powder and the lowering w/b. The mechanical strength and microstructure of reactive powder cementitious materials with low w/b can be expressed well by the A.C impedance characteristic parameters.

Abstract: The influencing factors of sodium sulfate solution physical crystallization attack on cement mortars were investigated through analyzing the changes of macroscopical capability and microstructure of cement mortars in attack process. Results indicate that with partial soaking time increasing, more and more sulfate sodium crystals grow on cement mortars surface, and cement mortars surface is denuded gradually. Compressive and flexural strength increase first and then decrease in the deterioration process. In the attack process, porosity of cement mortars decreases first and then increases. Lots of sodium sulfate crystals accumulate in pores of cement mortars and crystallization pressure is on the rise, resulting in physical crystallization attack taking place.

Abstract: According to the method of semi-immersion in 5% sodium sulfate solution, the property against sulfate attack of cement-based materials with various compositions are studied with the indexes of the amount of crystal salt in unit exposing area and the ratio of total mass change. The experiment indicates that the order of mortar with w/c=0.4 against sulfate attack from high to low are SAC 42.5>PO 42.5>Clinker>HAC 42.5. When w/b is constant and the cement was replaced by the same quantity of salic material, the order of mortar against sulfate attack are Clinker> PO 42.5> SAC 42.5> HAC 42.5. The replacement of SAC and HAC with the same quantity of salic material leads to the sharp decrease of its property against sulfate attack while the result is opposite for the clinker serial and PO 42.5 serial. Addition of redispersible polymer powder can lead to decrease of penetration and increase the properties of products to sulfate attack. Then, it comes to the conclusion that multi-binder with PO.42.5cement 70%–80% (quality percentage), and internal mixing of 5%–10% silica fume, 10%–15% fly ash can meet the high corrosion resistance requirements.

Abstract: The deterioration on sulfate attack was investigated both in physical crystallization and the chemical erosion. Specimens that suffered long-term immersion and dry-wet cycles in saturated sodium sulfate solution are compared to trace the physical attack. And the chemical erosion was conducted by comparing specimens which have been suffered long-term immersion in saturated sodium sulfate solution and saturated limestone solution. In the investigation, the non-destructive detecting indexes, such as the ultrasonic velocity, and the dynamic modulus of elasticity were measured. The permeability, the porosity and mechanical strength at 28-day age were measured. The flexural/compressive strength was measured after 90 wet-dry cycles. And then all the specimens were cut into cubes to take the measure of compressive strength. Based on the experiments, feasibility of various parameters, such permeability, relative dynamic modulus of elasticity, ultrasonic velocity and relative flexural/compressive strength, were investigated to evaluate the concrete deterioration. The results indicate that there is a close relationship between the deterioration by sulfate attack and concrete permeability, so the reduction of permeability is effective in promoting the resistance. The index of the resistance expressed by the dynamic modulus of elasticity ratio is comparable to that expressed by the relative flexural strength. A novel method was suggested in evaluating concrete by sulfate attack, namely, combined with some mechanical tests, the parameter of relative dynamic modulus of elasticity can be used to evaluate the deterioration; the permeability denoted as the amount of transporting charges within 6 hours can be used to evaluate the properties to sulfate attack.