This study investigated the strength properties of commercially manufactured sandcrete blocks in four cities in Southern Nigeria. 12 sandcrete block firms were visited and ten sandcrete block samples were randomly selected from each of these firms and taken to the laboratory for testing. Two sets of control samples were produced in the laboratory using mix ratios of 1:8 and 1:6. Aggregates used for all the block molding were also collected and their particle size analysed. Compressive strength of blocks from the 12 firms visited ranged from 0.19 to 1.32N/mm 2 and were far below the minimum specified values by NIS 87:2007.Authors ascribe this poor strength to noncompliance to standard. Compressive strength of the control samples revealed that complying with NIS 87: 2007 mix ratio and neglecting some other specified details is still not likely to produce standard products.
This paper presents an experimental study on the influence of ambient relative humidity on tensile creep of plain concrete amended with Ground Granulated Blast-furnace Slag and compares it with its influence on compressive creep. Tensile and compressive creep tests were carried out on concrete specimens of 34.49MPa compressive strength and 0.56 water/binder ratio at 51, 68 and 100% relative humidity. The results show a linear relationship between compressive creep and relative humidity; this cannot be said about tensile creep. Tensile creep was observed to be more sensitive to change in ambient humidity than compressive creep. Based on equal applied stress, tensile creep was found to be several times higher than compressive creep and the difference was greater in drying creep than in basic creep. On the basis of equal stress/strength ratio, tensile-to-compressive creep ratio was slightly less than 1 for drying creep and much less for basic creep.
This paper presents an experimental study on workability and compressive strength of concrete using various combinations of lateritic sand and quarry sand as complete replacement for conventional river sand fine aggregate. Quantity of lateritic sand varied from 0 to 50% against quarry dust at interval of 10%. Concrete cubes were prepared for two mix ratios: 1:1.5:3 and 1:2:4 and three water/cement ratios: 0.5, 0.6 and 0.7 and were cured and tested in the laboratory for compressive strength. Slump tests were also carried out for each mix. For each mix and water/cement ratios, control samples were also prepared using river sand as fine aggregate. The resulting concrete cubes fall within the range for normal weight concrete and although laterized quarry dust concrete had poorer workability, their compressive strength compare favourably with those of conventional concrete. The use of laterized quarry sand concrete for structural members is therefore recommended when laterite content is not more than 50%.
The pretreatment of 7- and 10-year-old Acacia mangium wood using incision, forced-air dying, and pressure were conducted to evaluate the effects on wet pockets, the drying rate, and drying defects. Quarter and rift sawn boards were used in this study. Results showed that the incidence of wet pockets in the incised, forced-air drying, and pressure-treated quarter and rift sawn boards of 7-year-old A. mangium alleviated up to 35% and 79%, 60% and 54%, and 54% and 82%, respectively. In 10-year-old A. mangium, the occurrence of wet pockets was reduced by 68% and 60%, 31% and 73% and 82% and 73% in quarter and rift sawn boards, respectively. Drying rates of 7-year-old A. mangium pressure-treated boards increased by 5% and 40% in quarter and rift sawn boards, respectively. The drying rate was 10% faster for 10-year-old A. mangium pressure-treated boards. The application of the pressure pretreatment yielded no severe drying defects at the end of the drying period, except for a mild collapse in one of the 10-years old A. mangium sample boards. Incision and forced-air drying pretreatments improved the drying rate; however, pressure treatment was found to be superior in reducing wet pockets and drying defects.
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