You Jun Xie

Application of Non-Destructive Technology in Evaluating Concrete to Sulfate Attack

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.

Study on Strength, Shrinkage and Creep of Concrete Containing Ultrafine Fly Ash Composites

At steam curing and moist curing conditions, the mechanical properties of concrete with different fineness and different proportions ultrafine fly ash-slag composite were studied. The experimental results indicated that the addition of ultrafine fly ash-slag composite had improved the long term mechanical properties of steam-cured concrete. The concrete with ultrafine fly ash-slag composite has lower drying shrinkage and creep compared to that of control concrete.

Efficiency of Scrap Rubber Particles on Strength of Cementitious Materials

An extensive research programme was set up to investigate the efficiency of scrap rubber particles on strength of cementitious materials. The index of strength loss rate of paste and mortar sample caused by increasing 1% volume rubber particles was proposed to analyze the efficiency of rubber particles in cementitious materials. And the corresponding mechanism was also discussed in this paper. Results indicate that in the investigated area, the loss rate in compressive strength both for paste and mortar almost ranges from 2% to 5% caused by increasing 1% rubber particles depending on the total volume of rubber particle added into sample. However, the loss rate in flexural strength of mortar by increasing 1% volume rubber particles is obviously different from that. Three roles of scrap rubber particles played in cementitious materials, named as deformation effect, equivalent-pore effect and hydrophobic effect, are responsible for the efficiency of scrap rubber particles on strength of cementitious material. The efficiency of rubber particles on strength of paste and mortar differs from each other due to the different microstructure between paste and mortar.

Water Sorptivity and Permability of New-Old Concrete Composite System

Several experiments were carried out to investigate the effects of water to binder ratio(w/b) and mineral admixtures on water sorptivity and permeability of new-old concrete composite system in this paper in order to further understand the transport properties and thus degradation mechanism of new-old concrete repair system. Results indicate that a reasonable choice of w/b of new concrete is of great importance for obtaining new-old concrete composite with a low water sorptivity. Addition of ultrafine powder such as silica fume as one of component of repairing materials will benefit for effectively reducing water sorptivity and permeability of new-old concrete repair system in practice. The linear correlative coefficient between capillary sorption coefficient, coulomb electricity and porosity of new-old concrete composite sample is bad and lower compared with those of corresponding new concrete samples. The total porosity of new-old concrete composite sample is not an exclusive factor determined its water sorptivity and permeability. The pore structure of new-old concrete composite sample, especially interfacial transition zone between new and old concrete plays more important role on transport properties of sample.

Experiment on Cement-Based Materials with Various Compositions against Sulfate Attack

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.

Thermal Deformation of Cement-Asphalt Mortar under Repetitive Heating and Cooling

Cement-asphalt mortar interlayer plays an important role in ballast-less track in high speed railway. Cement-asphalt mortar undergoes repetitive changes in temperature when it is exposed to its service environment. Change in temperature has a significant effect on the thermal deformation of cement-asphalt mortar, and even affects directly the durability of ballast-less track. In the paper, length and mass of the specimens of cement-asphalt mortar were continuously measured during the heating and cooling cycles within the range of temperatures of -10~60°C. The results indicate that there is an evidently irreversible shrinkage at the end of the first cycle of heating and cooling. The shrinkage taken place at the end of cycles of heating and cooling decreases with the increase in cycle numbers. Apart from the curve for the first heating, deformation curves of cement-asphalt mortar either for heating or for cooling are nearly lines. After being heated and cooled for 5 times, the temperature-deformation curve for heating nearly overlaps the curve for cooling. The percent of moisture loss at the end of every cycle decreases with the increase in cycle numbers. Thermal shrinkage occurs at about 0°C in the first heating.

Development of Cementitious Materials with High Resistance to Sulfate Attack by a Combination of Emulsified Asphalt and Fly Ash

Attack of sulfate crystallization and chemical interaction between sulfate and hydration product is one of the most important factors responsible for degradation of cementitious materials. This study investigates the effects of emulsified asphalt and fly ash as well as their combination on resistance of mortar to physicochemical attack of sulfate in order to develop high performance cementitious materials with high resistance to sulfate attack. The partly-submerged experiment with 5% Na2SO4 solution is designed to simulate physicochemical attack of sulfate salt on sample. Results indicate that, compared with fly ash, addition of emulsified asphalt is more effective in improving the resistance of mortar sample to physical crystallization role and chemical attack of sulfate. Moreover, a combination of fly ash and emulsified asphalt can further enhance the resistance of cementitious materials to physicochemical attack of sulfate, which results from the improvement of microstructure, reduction of CH product and increase of ductility of sample.

A.C Impedance Spectrum and Microstructure of Reactive Powder Cementitious Materials with Low w/b

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.

Corrosion Products in Cement-Based Materials under Sulfate Partial Soaking Attack

The deterioration mechanism of sulfate attack on cement- based materials under partial soaking condition is very complex. This paper investigated the surface morphology, microstructure and corrosion products in different zones of cement mortar under 5% sulfate solution partial soaking condition at 360 d by methods of SEM, EDS and XRD, respectively. Results show that under partial soaking condition, cement mortar are distinguished four zones – soaking zone, wet zone, crystallization zone and dry zone. Corrosion products in soaking zone and wet zone are predominantly ettringite, showing chemical corrosion take place in those zones. Corrosion products in crystallization zone are gypsum and crystals of Na2SO4 and Na2SO4.10H2O, showing both sulfate chemical corrosion in high concentration and physical crystallization attack occur in this zone. However, there is no any corrosion product founded in dry zone.

Deterioration Evolutive Process of Cement-Based Materials under Sulphate Physical Crystallization Attack

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.