ASSESSMENT OF THE COMPRESSIVE STRENGTH OF SOIL CEMENT BLOCK EXPOSED TO NPK FERTILIZER

The large number of farmers, especially the rural farmers, make use of NPK fertilizer for farming. These farmers lack adequate storage facilities for storing farm products. This study is aimed at determining the compressive strength of soil cement blocks (SCB) in contact with NPK fertilizer with a view to study the chemical reaction and ascertaining the suitability of the SCB in the construction of ware houses for the storage of NPK. The SCBs were obtained from a Hydraform block firm constructing an estate in Kuje, LGA Abuja. A total of 150 samples of the SCB, the soil used to produce the SCB, obtained from the site in Kuje LGA. The properties of the soil that determines the cement content and properties of the blocks were investigated in accordance with BS EN 771-1:2011 and BS EN 772-1:2011 respectively. The shrinkage has a value of 5.8% and sieve analysis (clay and silt 0.95%) indicates that the cement content can be increased to improve the  strength  of  the  SCB.  The  wet  compressive  strength  (1.8N/mm2)  was  78%  of  the  dry

compressive strength (2.3N/mm2) and less than 80% as recommended by BS EN 772-1:2011. Chemical analysis of the cement, soil and NPK were carried out, a saturated solution of NPK was determined to produce different concentrations. The solutions were prepared and three blocks selected at random were immersed for 7 days, 14 days, 21 days, 28 days, 56days and 90days respectively to ensure adequate exposure to the NPK solution. The compressive strength tests shows that the behaviour of the control differs from those in the solution. It was observed that the control experienced leaching of calcium hydroxide from the cement paste with low compressive

strength of 1.64N/mm2. Whereas, the compressive strength of the SCBs in NPK solution was

higher at 7days (1.7N/mm2, 1.74 N/mm2, 2.12N/mm2, 2.13N/mm2, 2.11N/mm2). After 56 days and 90 days, a white layer was observed to form within the SCB exposed to high concentrations of NPK. This was related to the likely ions exchange reaction with calcium hydroxide. The SCB were found to be suitable for use in the construction of ware houses to store NPK fertilizer as long as the selection of the soil and block production was based on standard code and the structure is kept dry from moisture.