Early age performance evaluation of new-anti cracking functional materials of concrete on member scale

Early deformation cracking is a widespread problem in base concrete walls of high-rise building. In the view of material to solve concrete cracking at early age, new-anti cracking functional materials make it by reducing shrinkage and regulating hydration heat. In this paper, several groups of concrete members were designed to contrast the effect of the functional materials, and based on embedding sensors in concrete members, temperature evolutions and strain evolutions are obtained in outdoor. The results show that compared with reference concrete, the maximum temperature rise of concrete prepared with new-anti cracking functional materials not only was reduced, but only there are reasonably expansive deformation at early age which can compensate later shrinkage which will be very beneficial to inhibit cracking. Introduction Researches have shown that the possibility occurrence of cracks for basement slab is 10% in the all surveyed slab projects, while it’s over 85% in all surveyed RC walls [1].However, a number of high-rise reinforcement concrete buildings have been conducted in recent years. Due to the demand of high seepage resistance and durability, cracking control of base restrained concrete walls of such engineering plays a very important role on construction quality. It becomes more and more popular to use shrinkage-compensating concrete prepared with expansive agent, as an important ways to inhibit concrete structure cracking. However, the most researches on expansive agent focus on laboratory experiments, including the expansion mechanism [2-4] and stability [5-6] expansion rate [7-8] shrinkage-compensating efficiency [9-10], etc., though recently a few references were found about the field monitoring of base structures [11-13].In addition, few references were found about it for chemical admixture adjusting the hydration heating rate of cement (HR). However, real-time temperature history and deformation history can be measured by field monitoring on macro scale, but for a certain practical structure, it’s impossible to provide control group to compare the application effect of new-anti cracking functional materials properly. Besides, specimens in the lab usually are so small that there is no obvious temperature rise from hydration. Thus, in this paper several concrete members were designed to solve the problems above in order to simulate the heat environment of base wall. Experimental Campaign Geometry. An experiment monitoring for measuring early-age temperatures and strains on prismatic concrete members was carried out, satisfying the following condition: a) the prism is big enough so as to engender a heat generation potential to cause significant temperature and strain gradients similar to practical base wall, and b) meanwhile it should be small enough in order to be compatible with laboratory work. The dimensions of the concrete prism are 1m×0.8m×1m. Lateral faces and base of the prism were insulated with 2cm thick plywood formwork. Concrete casting and 5th International Conference on Information Engineering for Mechanics and Materials (ICIMM 2015) © 2015. The authors Published by Atlantis Press 731 the experimental procedures took place outside room to be in the atmospheric environment. Materials. New-anti cracking functional materials include calcium expansive agent with low alkali and high efficiency (HME-III) and cracking resistant additive (HME-V). Here HME-V is prepared with HME-III and a new chemical admixture adjusting the hydration heating rate of cement (HR). HME-III is used to compensate shrinkage of concrete, whose property is shown in Table 1. HR is a kind of polysaccharose substance with relative molecular mass of 3000-5000 which is faint yellow and odorless. On the one hand, HME-V can regulate hydration rate of cement and delay cement hydration process, so that heat emission condition of structures can be fully applied to weaken temperature rise and temperature drop rate, which is helpful to reduce cracking risk due to temperature deformation; on the other hand, HME-V can adjust expansive history to make it effective for the capacity of compensating shrinkage of expansive agent in the high performance concrete structures [14, 15]. HR is different from traditional retarding admixture, shown in Fig.1. Table 1. Physicochemical characteristics of HME-III Content Performance index Fineness(1.18mm sieve residue)/% ≤0.50 Total alkali charge/% ≤0.60 Amount of chloride ions/% ≤0.05 Setting time Initial setting 170 Final setting 345 Restraint expansion rate 7 days in water 0.031 28 day in the air -0.012 Compressive Strength 7d 32.2 28d 48.7 Concretes mixtures proportions. Concrete grade C40, the impermeability grade P8 were prepared in the concrete prism, while cement type I P.O.42.5R is adopted. According to properties of raw material and trial mixture in the lab, concrete batches produced from the mix given in Table2 had slumps close to 120 mm to meet the pumping requirements. Table 2. Concretes mixture proportions(kg/m) No. Basic ratio /kg/m New-anti cracking functional materials /kg/m C FA S G W HME-III HME-V 1# 320 90 753 1084 165 2# 320 82 753 1084 165 8.2 3# 320 81 753 1084 165 9.02 Monitoring. Unbounded elastic wire resistance type strain meters with internal resistive temperature sensor were used to monitor the strain and temperature behavior of the concrete (with a precision of ±0.5°C) at the same time and location. All these strain gages were embedded into concrete. Sensor positions are schematically shown in Fig.2.For every concrete member, these sensors were embedded at two positions, one in the 2cm from lateral faces, and the other at the center. The mold were prepared with plywood formwork which can keep warm and be similar to thermal environment of wall. Installing of stain gauges were completed before pouring of the concrete. Data acquisition started after casting. Because concrete were not solidified just after concrete placing, the reference points for deformation were selected at final setting. 0 1 2 3 4 0 1 2 3 4 he at r el ea se r at e/ w /g age/d Reference traditional retarder HR decrease by 56.8%