MATERIAL USED = Ordinary Portland Cement with two water-tocement ratios of 0.42 and 0.52, specimens cured in the controlled environments of 25, 46 and 65 C for temperature, and 30% and 90% for relative humidity, ,
METHOD MIXED = To prepare mortar samples, the components were weighed. The SP was added into water, and then the cement was poured into this gel gradually. The gel, cement and remaining water continued to be mixed until the sand was added, and mixing continued until proper integrity was achieved. The final part was the mechanical mixing to ensure consistency of mixture design. Mortar specimens with dimensions of 5 cm were made per ASTM C 109 [7]. Specimens were cast in two layers, and the vibration table was used for entrapped air removal. Then, specimens were demolded after 24 h and cured in calcium hydroxide-saturated water at 24 ± 2 C until testing time. River sand was used as the fine aggregate. The gradation was conducted in accordance with [11] as shown in Fig. 1. The water absorption, the fineness modulus, and specific gravity were 2.18%, 3.19, and 2415 kg/m3,PHYSICAL
PROPERTIES = -----------------------------------------
APPARATUS = SIEVE, MORTAR MOULD, XRF, HYDROOLIC TESTING MACHINE ,PERCOMETER, Rapid chloride migration test, WATER SPORTIVITY TEST, OPTICAL MICROSCOPY
RESULT = The overall void content in mortar is composed of three general types of voids: capillary voids, entrapped air voids, and water voids.
a lower rate of the concrete surface moisture evaporation and corresponded to a lower decreasing rate of DC measurements.
The average compressive strengths of specimens up to 28 days old. The compressive strength is developed in all mortar mixtures by aging.
the sorptivity indexes of samples cured at higher temperatures, which showed poor performances, improved significantly when exposed to 90% relative humidity. This was most apparent for the WSI that higher relative humidities, to some ext The petrographic examination also provided information on the amount of carbonation of the sample. A better cured concrete tended to show less carbonation but this finding may depend on the effect carbonation has on the permeability of the surface concrete. ent, provide additional curing for concrete structures.
CONCLUSION = 1. Moisture loss had a direct variation with temperature owing to the increase in water evaporation rate with the rise of temperature. It has an inverse variation with relative humidity due to low moisture diffusion and protective performance of high relative humidity in evaporation of water through the specimens. 2. DC values which can represent free water content in the specimens are influenced by the curing relative humidity and temperature. High relative humidity reduced the water evaporation through the surface, and it caused DC values to be high. Two factors of increase in curing temperature and development of hydration process reduced free water content in the specimens, thereby reduction in DC values observed. It is worth mentioning that increase in temperature accelerated water evaporation and also hydration process, which both led to a reduction in free water content.
- Curing under higher temperatures accelerated the hydration and caused the heterogeneous distribution of hydration products. This condition makes the structure more porous and induced microcracks in the structure, which was responsible for increment in water sorptivity and reduction in compressive strength of specimens. In contrast, high relative humidity helped the progress of hydration degree and made the structure denser and as a result reduction in water sorptivity and increase in compressive strength was observed.
- Rise in temperature caused evaporation of free water, which led to enhancement in shrinkage. But, it also changed the free water to bounded water through the acceleration of hydration process that can be influential in a slight reduction of shrinkage. However, in general, increase in temperature led to the growth of measured shrinkage. Furthermore, the positive impact of high relative humidity in the reduction of shrinkage through helping the prevention of water evaporation observed.
- Rise in relative humidity through the providing sufficient moisture helped the hydration development, which led to denser microstructure and reduction in DRCM values. Furthermore, the rise in temperature helped the acceleration of hydration and production of larger C-S-H magnitude that also led to a reduction of migration coefficient at the age of 28 days. However, it is anticipated that at longer ages, migration coefficient values increase with temperature rise due to the incomplete hydration that happened under high temperature.
- At long-term ages rise in temperature accelerated mobility of electrons, therefore increased the conductivity of specimens and reduced their electrical resistivity. Moreover, a rise in relative humidity provided higher moisture and facilitated movement of ions through the microstructure of specimens and decreased their electrical resistivity values.
- The microstructure study showed that the air content decreased with an increase in temperature. The magnitude of the capillary system is controlled by the w/c and the degree of maturity of the mortar samples. Lower w/c showed higher capillary voids compared. Moreover, samples which were cured under 90% relative humidity had lower capillary voids. A better cured concrete tended to show less carbonation.