Yong Ge

Effect of Inorganic Salts on Frost Resistance of Concrete

Effects of water-binder ratio and inorganic salt additive, including NaCl, NaNO 2 and Na 2 SO 4 , on frost resistance of concrete were investigated using the orthogonal experimental test. There were two criteria, i.e., the relative dynamic elastic modulus (RDEM) and weight loss that can be used to evaluate the resistance of concrete subjected to fast freeze-thaw tests. The results show that the effect of water-binder ratio on frost resistance of concrete is obvious and that the salts have different effects: adding NaCl and Na 2 SO 4 into concrete decreases frost resistance and that the worst effect occurs when the dosage of NaCl and Na 2 SO 4 is about 0.5% and 1.25% of cement, respectively. Adding NaNO 2 into concrete improves frost resistance but the effect is not obvious. The influential effects of these salts are ranked to be NaCl>Na 2 SO 4 >NaNO 2 .

Effect of Saturation Degree on Concrete Deterioration due to Freeze-Thaw Action

Freezing-thawing durability of cement concrete is extremely important in cold weather, to better understand mechanism of frost damage and air-entraining，saturation degree of pores in concrete and its relation with frost resistance were studied in this paper. Concrete specimens with different saturation degree from 0 to 100% were prepared used a sealed tin with a high water pressure pump. Then these specimens were subjected to six freezing-thawing cycles and the relative dynamic modulus of elasticity was examined. The results showed that critical saturation degree of concrete with water- binder ratio of 0.30 and 0.47, air content of 1%, 4% and 6% were from 0.60 to 0.80. When its saturation degree exceeded the critical value, concrete was deteriorated significantly after only six freeze-thaw cycles. The critical saturation degree was mainly related to the air content of concrete mixture, and it decreased with the increasing of air content. The difference between the saturation degree and the critical value can be used to evaluate potential frost resistance of concrete, and its result was consistent with the result of frost tests very well.

Deterioration of Concrete Freezing-Thawing in Different Salts Solution

The frost resistance of concrete subjected to 3.5% NaCl solution, 5%, 7%, and 10% Na2SO4 solution and seawater were investigated by quick freeze-thaw test. There were two criteria, the relative dynamic modulus of elasticity (RDME) and the mass of scaling, for evaluating the frost resistance of concrete. The results showed that scaling was the main characteristic of deterioration when concrete subjected to freeze-thaw cycles in 3.5% NaCl solution and seawater, whereas RDME had little change. When freezing and thawing in Na2SO4 solution, concrete failed because of internal damage and surfaces of lower strength concrete specimens appeared local swelling and scaling before failure. Concentration of Na2SO4 solution had influence on frost resistance of concrete: deterioration of concrete in 5% or 7% Na2SO4 solution was severe but slower when the concentration reached to 10%. Entraining air into concrete was the best method to improve the durability of concrete subjected to freeze-thaw cycles in all solutions.

Mechanical Properties of Concrete Containing Ceramsite Sand

Lightweight aggregate concrete has been widely used due to its excellent performance, such as the light weight, the high strength and the thermal insulation. Ceramsite sand is a kind of artificial fine lightweight aggregate, which could be used as an effective internal curing material for concrete with low water-binder ratio. In this paper, the mechanical properties of concrete with the water to cement ratio of 0.3, 0.35 and 0.4, in which the natural sand was replaced by ceramsite sand at 20%, 40%, 60%, 80% and 100% in volume were studied. The hydration degree of cement in the paste around ceramsite sand particles was also tested. The research results showed that with the increasing of the ceramsite sand content, the compressive strength, the flexural strength and the static elastic modulus of concrete decreased. Ceramsite sand promoted the hydration degree of cement at the interface area, and this effect became more obvious for the concrete with lower water to cement ratio.

The Research of Influence on the Freezing Resistance and the Permeation Resistance of Concrete With Spraying Silane

Silane, as an extremely hydrophobic material, changes concrete surface from hydrophilic state to hydrophobic state by spraying on the surface of concrete. It has the ability to block the external corrosive medium to improve the durability of concrete. Three types of strength grade of concrete (C30, C40, C50) were designed, after spraying with silane on the surface of concrete, to measure the penetration depth of silane and the influence on water-absorption rate, liquid-absorption rate, chloride ion diffusion coefficient and salt frost resistance. The test result shows that: by spraying silane on the surface of concrete,the one hour water-absorption rate of concrete was reduced by more than 98%, the 48 hours water-absorption rate was cut down above 91%, and the 48 hours liquid-absorption (3% NaCl solution) rate was decreased above 94%. The penetration depth for C30 and C50 has the maximum value (6.3mm) and minimum value (3.9mm) respectively. Absorption reduction rate of chloride ion overall was decreased by above 93%, and chloride ion diffusion coefficient was reduced by 42% ~ 48%. The freeze-thaw resistance was improved by 5 times. Key words: silane, the salt frost resistance, liquid-absorption rate, chloride ion diffusion coefficient

Effect of Mineral Additives on Internal Relative Humidity and Dry Shrinkage of Light Weight Aggregate Concrete

Effect of fly ash and slag on internal relative humidity (IRH) and dry shrinkage of light weight aggregate concrete (LWC) are studied in this paper. As indicated in this test, mixed with mineral additives can reduce dry shrinkage of concrete. The more volume of fly ash and slag ash, the lower decrease speed of IRH is, which contribute to the decreases of dry shrinkage rate too. At the same curing-age and dosage, the relative humidity inside the fly ash concrete is higher than the slag one. As consequence, the rate of dry shrinkage of fly ash concrete is lower than slag concrete. Also, there is a significant linear correlation between the lowered values of IRH and dry shrinkage rate.

Influence of Air Content and Vibration Time on Frost Resistance of Air Entrained Concrete

Air-entraining agent turely is one of the necessary compositions of the high durability concrete. The influence of air content and vibration time on the frost resistance of concrete was researched, and air void characteristics of hardened concrete was analysed. The results showed that the air contents could reduce the compressive strengthof hardened concrete excessively, but it made the spacing factor reduce obviously and significantly improve the frost resistance of concrete.The air voids with different structure in concrete were realized by vibration time. It was found that the air void structure and the frost resistance properties were influenced by the vibration time largely. The optimized vibration time is 30s, the appropriate vibration time is 20s~30s, no more than 35s.

The Flexural Strength and Frost Resistance of Air Entrained Concrete

The flexural strength and frost resistance properties of air entrained concrete were tested in this study. Although the flexural strength of concrete does not change largely with increasing of air content, it still has a maximum value with air content of 4%. The test results show that the frost resistance increase with increasing of air content. In air entrained concrete, the total air content is not the only factor that affect the final properties of the concrete, the air void structure parameters, including void size, shape, and distribution, are key factors as well. It was found that the air void structure and the frost resistance properties were influenced by the vibration time largely. The optimized vibration time is 30s.

The influence of admixtures on vibration viscosity coefficient of pavement concrete

In this paper, the influences of common admixtures including air entraining agent, superplasticizer, shrinkage-reducing agent, retarder, fly ash and slag on vibration viscosity coefficient of fresh concrete were analyzed. The results showed that the vibration viscosity coefficient of fresh concrete was markedly decreased when using UNF-5 naphthalene formaldehyde sulphonated superplasticizer. When SJ-2 air entraining agent, SZ103 shrinkage-reducing agent, retarder and slag were used, the vibration viscosity coefficient of fresh concrete was also reduced. But when fly ash was added, the vibration viscosity coefficient of fresh concrete was increased.

Effect of Low Temperature on Mechanical Properties of Concrete with Different Strength Grade

The effect of low temperature (-35°C) on the mechanical properties of concrete with different strength grade such as compressive strength, flexural strength, splitting tensile strength and elastic modulus was studied. The results showed that all of the mechanical properties were improved at -35°C. It was also can be found from the tests, as the strength grade increased, the growth ratios at -35°C of compressive strength, flexural strength and splitting tensile strength decreased. But the growth ratio of elastic modulus increased with the increasing of strength grade.