No abstract

In Indonesia, several regions have a minimum quantity or none of fresh water. Self Compacting Concrete (SCC) has a dense microstructure. Knowledge about the microstructure and properties of the individual components of concrete have a relationship that is useful for controlling the behavior of concrete. Porosity and microstructure SCC using sea water as mixing water and curing water discussed in this paper. The results showed the higher the compressive strength of SCC sea water is getting smaller porosity. Porosity on the SCC decreases with increasing quantities of microstructure phase tobermorite (CSH), portlandite (CH), Friedel's salt and ettringite.

Abstract. Properties of fresh concrete made in tropical countries, which is mixed, transported (with agitation), placed and initially cured in places where the temperature ranges from about 20 o C to 40 o C and relative humidity above 60%, are not completely understood. Applicable requirements also differ from country to country and government agencies and private enterprises have their own specifications. Assuming such temperature and relative humidity conditions, the present study is an attempt at evaluating the properties of hot weather concrete in fresh state with using a method of ready-mixed concrete. The fresh concrete was mixed and agitated at varying concrete and ambient temperatures. Three groups of the component materials, each material having such temperature as to bring resulting temperature of the fresh concrete to about 20 o C, 30 o C, 35 o C, were chosen. The temperature of cement was conditioned to about20 o , 40 o C and 60 o C for each of groups respectively. The aggregate was made warm enough to simulate the condition of outdoor pile in ready-mixed concrete plant. The temperature of tap water was always 20 o C as it was easily controlled and unlikely affected by outdoor temperature. With the fresh concrete prevented from evaporation, slump loss is caused solely by increased temperature of concrete. During agitation, the slump loss increases rapidly during the first 30 minutes but moderately during the remaining period. Concrete-placing temperature (upon arrival at the work site) could be estimated by a proposed formula derived from this study. Besides the freshly mixed concrete temperature, this formula also takes into consideration the ambient temperature, agitating time in transit and hydration heat. The achievement as described in this study may be useful to control concrete quality in terms of strength, shrinkage and other properties of concrete to be placed in hot-humid environment.

Indonesia is an archipelagic country which makes many areas doesn't have qualified water as drinking water. As concrete construction building in the region has possibly minimum or non-existent amount of fresh water, the using of sea water in mixing concrete and curing concrete is unavoidable. The demand of water is getting more and more increasing in both the improvement of infrastructure development and the life need. In the concrete industry, several billion tons of water is used as water mixing, curing and cleaning every year. Therefore the use of seawater is not allowed. In fact, we know that seawater is one of the abundant natural resources. Due to this problem, the research on the use of seawater is very important owing to the saving of freshwater is seriously needed. This study uses seawater by combining effective and efficient concrete technology of Self Compacting Concrete (SCC). This paper is a part of ongoing research studying about microstructure characteristics and the strength of SCC using seawater. It discusses about the compressive strength, absorption and porosity as microstructure characteristics of SCC until the age of 28 days. The results are: (1) the seawater used as mixing water did not affect the development of the compressive strength of concrete, (2) the difference compressive strength of SCC-SS with SCC-FF at an early age is very high occurred at ages 1 and 3 days and (3). The higher the compressive strength value is, the smaller the absorption and porosity is in concrete.

The compressive and tensile strengths of concrete made in hot weather condition decreased due to loss of mixing water caused by high evaporation. One method to overcome the problem is the use of saturated fly ash aggregate. The water content in fly ash aggregate can flow out to the hardened cement paste to continue the hydration process. This "self-curing" mechanism could produce more hydration around the surface of fly ash aggregate which subsequently increases concrete strength. Experimental study has been conducted in temperature of 20 o to 40 o with humidity of 70% for dry curing, water curing, and nearly 100% for fog curing. Effect of self-curing could be justified as the strengths of concrete using fly ash aggregates is higher than concrete using fly ash aggregates covered with silane agent, and crushed stone aggregates. Even in high temperature, the self-curing could increase the strengths of concrete due to bond strength around the surface of each fly ash aggregates.