Use of lunar type soil for concrete construction

The objective of this research program was to study the feasibility of making quality concrete with soils for regions where construction sand and aggregates are in short supply, for example, lunar construction. Mitchell et al., reported that lunar soil had substantial variability in type and properties. Hence five different soil types were used in this study. A control concrete mixture with standard sand and eleven other mixes with soil were prepared. A cement, sand or soil, and coarse aggregate ratio of 1:1.5:1.5 by weight was used. The sand replacement was either 100% or 50%. The variation of density and strength of soil concrete with water content was investigated to obtain suitable water cement ratios for soil concrete. The test results showed that the variation of density with water content was as that for compacted soils. With the increase of water content the density of soil concrete increased. Then it decreased beyond an optimum water content value. The experimental results showed various optimum soil cement ratios with maximum soil concrete densities for different soil types. Soil concretes produced at its optimum water cement ratio had the highest compressive strengths. These optimum water content values were used in a detailed study of the pozzolanic reaction in soil concrete. The test results showed that except for the two clays all other mixtures developed had more than 50% of the 28 day strength after seven days of curing. However, the one day strength varied from 15% to 33% of the 28 day strength. Therefore, it may be concluded that there is a delay in pozzolanic reaction due to soil in concrete, and soil concrete needs more than seven days to gain substantial strength. The compressive strength test results show that all soils mixes produced concrete with compressive strengths higher than 17237 kPa (2500 psi) except for the mix having 100% of clay. Therefore, all the soil types except clays may be used to make concrete. The durability test showed that all soil concrete types continued pozzolanic reaction beyond the 28 days.