The Influence Of Calcium Nitrate On The Compressive Strength Of Concrete Exposed To Freezing Weather

Based on ACI 306R-88, the minimum temperature necessary for maintaining concretehydration and strength gaining is 50C. If the atmosphere weather becomes lower than 50Csome preserve measurements should be taken in order to prevent decrease in the rate ofhydration and to prevent fresh concrete from freezing. Most of the cold weather livingcountries spend annually plenty of money in order to facilitate concrete placing in the coldweather and to extend the construction season. It has been tried to carry out the behavior of fresh and hardened concrete contained calcium nitrate at different curing temperatures below freezing temperature of water and compare the results with the both control samples and real Erzurum winter conditions. For this reason, calcium nitrate is used at level of 6% by weightof cement dosage in the mixes. After casting, one group of concrete samples were cured in the different deepfreezes at -5,-10,-15,-200C for 7, and then that same samples were cured inwater for 28 days. With usage of calcium nitrate in the mixes, compressive strength of concrete increased between 96-297% at -50C, -100C, -150C and -200C, when compared tomixes without antifreeze admixtures that 7 days only freezer cured and 28 days water curedafter 7 days freezer cured, respectively. The results showed that it is possible to use calciumnitrate as an antifreeze admixture in concrete placing process in cold weather concreting

A study on the compressive strength and microstructure characteristic of alkali-activated metakaolin cement

The main purpose of this study was to investigate the compressive strength and microstructure characteristicof alkali-activated metakaolin cement (AAMC). In accordance with this purpose, besides the pure metakaolinactivation five other mixtures were designed by substitution of different OPC ratios instead of metakaolin(MK) from 0 to 25 (5, 10, 15, 20, 25% OPC). AAMC was activated with sodium silicate (Na2SiO3) ofmodulus Ms = SiO2/Na2O = 3.1 and NaOH solutions (32% of NaOH, 68% of water by mass). The ratio ofliquid/solid (L/S) was kept constant at 0.65. All specimens were cured at 70 °C for 72 hours then kept inroom conditions until the days that experiments were performed. Compressive strength and UPV experimenttests were carried out on all specimens at different curing periods of 3,14,28 and 90 days. In addition, themicrostructure of 28 days alkali-activated metakaolin cements were analyzed with scanning electronmicroscope (SEM). The results showed that AAMC specimens reached the desired strength and major part ofthe final strength was gained at the end of 3 days of curing.Keywords: Alkali activated cement; Geopolymer; Metakaolin, microstructure, UP