Papers by Keyword: Frost-Resistance

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Authors: Zhen Wu Shi, Shuang Liu, Rui Rui Zhang
Abstract: Based on the evaluation of fibrous concrete materials and the experiments of freezing-thawing resistance home and abroad, the present experiment takes relative dynamic modulus of elasticity and rate of mass reduction as an analytical index to conduct a comparative study on the effects of the mixing of four kinds of polypropylene fiber on the cement concrete freezing resistance. The results show that different kinds of polypropylene fiber have different influences on cement concrete freezing resistance. And some polypropylene can improve it while others may make it decreased.
673
Authors: Bing Du, Quan Xin Yi
Abstract: Aiming at influencing factors in the abominable natural environment in permafrost district of Qinghai-Tibet railway, according to different requirements on concrete’s durability performance which exerted by different climatic conditions and different environment of Qinghai-Tibet railway, the design and the construction on site of durable concrete was investigated.
197
Authors: Olga Pertseva, Sergey Nikolskiy
Abstract: The task of the project is obtaining the dependence between the relative decreasing of strength and rate of strain and substantiation of the new method for determination of concrete frost resistance. It has been analytically proved that using concrete’s rate of strain ε as a measure of damage, instead of decreasing of tensile strength R, increases freeze-thaw resistance’s accuracy of estimation a lot under otherwise equal conditions by the time of freeze-thaw cycling. Also it has been experimentally shown that ratio of relative decreasing R to ε in direction, perpendicular to compression, is assumed to be independent on values R and ε for a given concrete and on the ways of achieving them during mechanical or freeze-thaw cycling. To determine the dependence δR/R by ε (z) 8 specimens were tested by non-destructive method (RU 2 490 631) and two baths of 50 specimens by basic method (thermo cycling). Results of the non-destructive method are different from results by basic method for 6,3%. Dependence of relative decreasing in strength by rate of strain is near to linear and, therefore, value of z is constant. Taking this into account patented methods for estimation of concrete’s freeze-thaw resistance as per values R and ε received after freezing and thawing cycles of some specimens and their postlimenary failure by linear compression was substantiated.
505
Authors: Yong Ge, Wen Cui Yang, Jie Yuan, Bao Sheng Zhang, Ai Ling Xiong
Abstract: 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.
315
Authors: Li Juan Kong, Qing Chao Meng, Yuan Bo Du
Abstract: Influence of aggregate types on the impermeability and frost-resistance of concrete with different water/cement ratios were investigated, as well as the pore structure and hydrates of the ITZ. The results show that, concrete prepared with a high water/cement ratio and using granite aggregate, presents the highest values of chloride diffusion coefficient and the lowest numbers of freeze-thaw cycles. Whereas concrete prepared with a low water/cement ratio and using limestone aggregate, obtains the similar durability results. The limestone aggregate with a rough surface and higher water absorption, has a tight bonding with the cement paste. However, the granite and basalt aggregate that formed by magma eruption, have higher activity. The XRD results demonstrate that more clinkers participate in the hydration of cement, therefore, resulting in a denser ITZ. In order to improve the concrete durability, the basalt aggregate both with higher activity and rough surface is consider optimal.
1801
Authors: Wen Cui Yang, Yong Ge, Bao Sheng Zhang, Jie Yuan
Abstract: 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.
404
Authors: Mei Yan Hang, Wei Zhang
Abstract: In this paper, the frost resistance on different water-cement ratio of concrete after the air-entraining agent admixture. When the gas is controlled about 4%, with the lower water-cement ratio, freeze-thaw resistance of concrete is increased significantly. And then the frost resistance of YC20 and YC40 concrete which are mixed in efficient air-entraining water-reducing agent were studied, the experiment results that when the concrete YC40 reached F300, gas content reached more than 4.5%,and the strength without reducing, the durability would improve. But the YC20 is different, so, GL-B4-efficiency air-entraining water-reducing agent does not apply to the water-cement ratio above 0.6 of the concrete
3566
Authors: Lei Jiang, Di Tao Niu, Min Bai
Abstract: In order to study various factor affecting durability of steel fiber reinforced concrete (SFRC), basic experimental research that combine the action of freezing-thawing cycles and deicing salt to SFRC was conducted. In the experiment, the volume fraction of steel fiber and number of freeze-thaw circulation are taken as variable parameter. Based on the different numbers of freeze-thaw circulation, weight losing of SFRC, splitting strength and the dynamic modulus of elasticity were measured. Furthermore, the reinforced mechanism of the SFRC under the action of freeze-thaw was analysed. The test results show that after adding a certain amount of steel fiber to the concrete, cracks in concrete at early stage are effectively prevented and the permeability of concrete is obviously reduced, thus the durability of concrete is improved. The reinforced actions of steel fiber on splitting strength of concrete are notable and the influence of steel fiber volume fraction on the frost-resisting property is obvious. On the contrary, the negative effects of steel fiber with high volume fraction on the splitting strength of concrete exist. The best performance of SFRC can be got when the steel fiber quantity is 1.5%.
243
Authors: Lei Jiang, Di Tao Niu, Min Bai
Abstract: Based on the fast freeze-thaw test in 3.5% NaCl solution, the frost resistance of steel fiber reinforced concrete (SFRC) was studied in this paper. On the basis of scanning electron microscope (SEM) and mercury intrusion method, the microstructure and pore structure of SFRC was analysed. The reinforced mechanism of SFRC under the cooperation of freeze-thaw and NaCl solution was discussed. The test results show that adding appropriate amount of steel fibers into concrete can reduce the pore porosity and improve the compactness of concrete. The effects of steel fiber with proper volume fraction can inhibit the peeling of the concrete and reduce its damage rate. The volume of steel fiber on the frost-resisting property of SFRC is obvious.
357
Authors: Ying Zhang, Jiang Dong Cai, Shan Lin Xu, Zhi Jun Hu
Abstract: The influence of admixture on concrete pore structure was analyzed by using the mercury intrusion method and the rapid frozen-thaw method under the condition of the same water/binder ratio in this paper, and thus the relationship between pore structure and frost resistance of concrete were analyzed. When the compound mineral ad-mixture is mixed, the porosity rate of concrete can be decreased and the harmful hole is in-creased, the less-harm hole and the no-harmful hole are decreased. The early strength of concrete is not decreased. But the strength has the increasing trend in the late, which is more favorable for the impermeability and corrosion resistance. But the improvement of the freezing resistance is not obvious. The admixture of air entraining agent can increase the porosity and more-harmful hole, and the concrete strength will be decreased, which will be not favorable for the freezing resistance of concrete. If these two substances are admixed at the same time, the concrete porosity is increased, and the pore size distribution of concrete can be reasonable. The decrement of concrete strength is not obvious, but it is favorable for the freezing resistance of concrete.
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