Geotechnical and Geochemical Assessment of Natural Sands in Ahanta West Area, Southwestern Ghana

Geotechnical and geochemical assessment of natural sands being used as fine aggregates for construction purposes in Ahanta West and its Environs was carried out, as well as addressing the environmental problems associated with the exploitation of these sand through the sand winning activities. The results from geotechnical and geochemical tests were bench marked with British, American and Ottawa Standards for testing materials. Representative samples were taken from five different sand winning sites namely, Pompuni, Agona Banso, Fretsi, Tumentu stream and Fretsi river. The geotechnical tests carried out were specific gravity, grain size analysis, moisture content, silt content, permeability test using the constant head permeameter method. The photometer (Hydro Test HT 1000) was used to determine silica, sulphate and chloride concentrations in the sand samples. The oxides for the geochemical analysis were determined using the X-ray fluorescence (XRF) method. The results from the study areas showed that except for Fretsi, the specific gravity, grain size analysis, moisture content, silt content and permeability tests were within the acceptable range for natural sands. Sand samples from Pumponi and Agona Banso had the required Cu and Cc values of being well graded. Sulphate and chloride concentrations were within standards for all the samples;however, silica was low for all the samples. Fe2O3, Al2O3, MnO and Na2O did not meet the Ottawa sand standard. Natural sand is not recommended to be used for construction purposes however, these sands may be treated or blended if it is to be used for construction purposes. There are serious environmental implications for the sand-winning activities in the study areas such as stripped overburden, creation of pits and ponds, increased total suspended solids in surface waters, and destruction of aquatic habitats which needs to be addressed.

Effects of Manufactured-sand on Dry Shrinkage and Crccp of High-strength Concrete

The influences of natural sand, manufactured-sand （MS） and stone-dust （SD） in the manufactured-sand on workability, compressive strength, elastic modulus, drying shrinkage and creep properties of high-strength concrete （HSC） were tested and compared. The results show that the reasonable content （7%-10.5%） of SD in MS will not deteriorate the workability of MS-HSC. It could even improve the workability. Moreover, the compressive strength increases gradually with the increasing SD content,and the MS- HSC with low SD content （smaller than 7%） has the elastic modulus which approaches that of the natural sand HSC, but the elastic modulus reduces when the SD content is high. The influence of the SD content on drying shrinkage performance of MS-HSC is closely related to the hydration age. The shrinkage rate of MS-HSC in the former 7 d age is higher than that of the natural sand HSC, but the difference of the shrinkage rate in the late age is not marked. Meanwhile the shrinkage rate reduces as the fly ash is added; the specific creep and creep coefficient of MS-HSC with 7% SD are close to those of the natural sand HSC.