DETERIORATION OF CEMENT- BASED STRUCTURES: CHEMICAL INVESTIGATION OF CRACKS IN SANDCRETE BLOCKS

Abstract

Cement-based structure stability could be characterized not only by their mechanical strength, soil geophysics and loading conditions, but also the resistance to various physical and chemical factors that could initiate its deterioration. The contribution of water and various water -based solutions in the environment, to cement based structure durability could be either physical as in seasonal flooding of the structure or chemical often initiated by the presence in the solution of organic, inorganic compounds and gases. Irrespective of the deterioration type, its destructive effect could be attributed to the build up of internal stress and weakening of the structure matrix. This work investigated the role of chemical changes in the sandcrete matrix in the formation and developn1ent of macrocracks in cement based sandcrete walls. Collected sandcrete samples were analyzed using titrimetric, gravimetric and instrumental methods. Results showed. that the difference in percentage composition of Si02 at the top to bottom were high ranging from 76.72 to 80.30 % in all the sandcrete blocks samples analyzed. This indicates high permeability of ground level structure by the soil waters. The acidic nature of the soil in some areas with pH varying from 5.89-6.11 could seriously undermine the strength of the structures. The percentage compositions of CaO were generally very low ranging from 3.83 % at the ground to 4.44 % at the top level. Na20 records high composition at the top level declining steadily to the ground level (0.80 - 0.68 ~o). This may lead to Alkali Silica reaction. There are compositional differential horizontally and vertically across most points. This can be attributed to chemical reaction involved between the oxides of CaO, MgO, Na20, S03 with surrounding compounds in the presence of moisture, or poor cement quality, or probably cement with quality that does not comply to standard requirements.