CONCRETE

This study investigated the effect of nanosilica (NS) as a partial replacement for ordinary Portland cement (OPC) on the mechanical and durability properties of concrete. The aim was to assess the suitability of nanosilica in improving concrete performance and to determine its optimum replacement level for sustainable construction applications in Nigeria.Concrete was produced using a nominal mix ratio of 1:2:4 and a constant water–cement ratio of 0.5. Nanosilica was used to replace cement at levels of 0%, 1%, 2%, and 3% by weight. Tests carried out included slump test, setting time determination, compressive strength test, flexural strength test, and water absorption test. Statistical analysis of the results was performed using oneway analysis of variance (ANOVA).Results showed that workability increased with increasing nanosilica content, while both initial and final setting times decreased. Compressive and flexural strengths increased up to an optimum nanosilica content of 2%, where 28-day values of 24.4 N/mm² and 5.25 N/mm² were recorded, compared to 22.5 N/mm² and 4.67 N/mm² for the control mix. Water absorption reduced to 7.3% at 2% nanosilica replacement compared to 9.7% for the control, indicating improved durability. ANOVA results showed no significant differences in compressive strength, flexural strength, and workability (p > 0.05), while setting time showed significant variation (p < 0.05). The study concluded that 2% nanosilica replacement provided the best overall performance and is recommended for producing stronger and more durable concrete

The high cost of concrete materials in building projects has been a concern in Nigeria. This project was carried out to investigate and compare the use of Palm kernel shell and Coconut shell in replacement of coarse aggregate in 1:1:2 concrete mix design and 0.5 water/cement ratio. It aimed at determining the maximum partial replacement of by Palm kernel shell and Coconut shell in concrete and comparing their compressive strength and other relavant mechanical properties. A total of 143 cubes of size 100mm × 100mm × 100mm were casted, the test conducted include: Sieve analysis test, Workability (Slump) test, Density test, Compressive strength test and Water absorbion test. From Sieve analysis result obtained, the values obtained shows that the PKS is poorly graded and will contain lot of voids while the CS contain smaller void. From the slump test results, true slump was obtained for both PKS and CS as coarse aggregate replacement as the slump values were within 7-42mm which is medium workability range, although the CS concrete had higher slump compared to PKS. Both Palm kernel shell and Coconut shell concrete had density greater than 2000kg/m³ for light weight concrete, the results shows that PKS concrete has lesser density compared to CS concrete, meaning it offers better sound insulation and fire resistance. The results shows that for PKS concrete the maximum compressive strength obtained and is useful was 21.93N/mm² (25% replacement) but with poor workability , moreover the useful maximum compressive strength for CS concrete was 20N/mm² (40% replacement) but with poor workability. The results also showed that the useful maximum compressive strength of PKS concrete and CS concrete with good workability was 28.63N/mm² (5% replacement) and 29.48N/mm² (5% replacement) respectively. CS as coarse aggregate had an appreciable strength compared to PKS as a coarse aggregate in concrete, considering strength/economic ratio, Coconut shell is recommended to be used as a partial replacement of coarse aggregate in making light weight concrete. The cost benefit analysis showed that 40% replacement with Coconut ahell in 1m³ of concrete there is a savings of #3,120 and at 35 replacement with In 1m³ of concrete there is a savings of #4,452.

The aim of this project is to determine the effects metakaolin powder has on the mechanical properties of concrete when partially replaced at various percentages (15%, 20% and 25%). The idea behind this study is to assess if metakaolin powder can serve as a suitable substitute for sand as a fine aggregate in terms of responses to various tests. This study seeks to serve as a guide for future research in this field. It also serves to answer the question of why seek substitutes for fine aggregate at all.The tests required for accomplishing this experiment’s objectives are the compressive, flexural, slump and density tests, to determine the compressive strengths, flexural strengths, workability and density, respectively, of various samples been tested. Conventional concrete samples are cast and compared to partially replaced concrete to analyze the effects on concrete. The results for various tests differ showing rises and falls in strengths, slumps and densities. These results are then compared using tables and charts, from which a conclusion is drawn. The conclusion drawn for workability is that it has a low workability due to the pozzolanic nature of metakaolin powder and its reaction to cement and for the strengths, it is ascertained that concrete samples experience an increase in strength at 15% of partial replacement followed by a decrease at 20% and an increase at 25% indicating a possibility of later strengths at higher percentages but more so at longer periods of curing.

This study presents a comparative evaluation of the strength characteristics of concrete using both non-destructive (rebound hammer) and destructive (compressive strength) testing methods. The primary aim of the research was to determine the correlation between rebound hammer readings and actual compressive strength values of concrete produced from different mix ratios; 1:2:4 (C20), 1:1.5:3 (C25), and 1:1:2 (C30) under proper compaction and curing conditions. The investigation was motivated by the need to establish a reliable, quick, and non-invasive method for assessing the in-situ strength of concrete structures while maintaining compliance with international testing standards. The experimental program involved casting 100 mm × 100 mm × 100 mm concrete cubes for each mix ratio. The cubes were cured for 7, 14, and 28 days, after which they were tested using a Schmidt rebound hammer in accordance with BS EN 12504-2:2012 and ASTM C805, and a compressive testing machine following BS EN 12390-3:2019. In addition, a sieve analysis was performed on both fine and coarse aggregates to determine their particle size distribution and compliance with BS 812 (Part 103.1:1985) standards. Statistical regression analysis was also conducted to develop mathematical relationships between rebound number and compressive strength, and to determine the coefficient of determination (R²) for each mix ratio. The results indicated that concrete strength increased consistently with both higher cement content and longer curing periods. At 28 days, average compressive strengths of 17.89 N/mm², 25.92 N/mm², and 31.52 N/mm² were recorded for C20, C25, and C30 grades respectively. The rebound hammer results were found to underestimate compressive strength by about 5–10%, but showed a strong correlation, with R² values of 0.85 (C20), 0.96 (C25), and 0.98 (C30). The findings confirm that while the rebound hammer test cannot replace compressive testing for structural verification, it is a valuable non-destructive tool for rapid field assessment and comparative strength evaluation. Proper calibration using laboratory data is essential to ensure reliable application in insitu concrete quality control

This experiment studies the effect of waste ceramic tile aggregate as partial replacement of conventional coarse aggregate on the compressive strength and durability of concrete, in an attempt to determine the possibility of utilizing waste ceramic tile aggregate (WCTA) as partial replacement for conventional granite in concrete production. For the experiment, a M25 grade concrete with a water/cement ratio of 0.5 was prepared using granite substituted with WCTA at a replacement percentage of 0%, 10%, 20%, 30%, 40% and 50%. Tests such as sieve analysis and aggregate impact value was performed on the various aggregates used in the study to determine their suitability. Concrete cubes of size 100mm×100mm×100mm were casted and tested for compressive strength after a curing period of 7 and 28 days. Water absorption test was also performed on the hardened concrete mixes to determine their durability. From the experimental results, it is found that the 7th day compressive strength of the concrete mixes are 21.32N/mm², 25.37N/mm², 23.54N/mm², 24.20N/mm², 22.21N/mm² and 20.47N/mm², while 28th day compressive strength is found to be 29.66N/mm², 29.80N/mm², 31.94N/mm², 33.59N/mm², 29.65N/mm² and 27.80N/mm², for 0%, 10%, 20%, 30%, 40% and 50% substitution respectively. Also the water absorption of the concrete samples is observed to be 2.36%, 2.47%, 2.21%, 1.64%, 1.98% and 2.14% for 0%, 10% ,20% ,30%, 40% and 50% respectively. The result reveals that the use of WCTA as partial replacement of coarse aggregate in concrete leads to the enhancement of the compressive strength of concrete, as long it doesn't exceed 30% replacement. Also the addition of WCTA leads to an increase in the water absorption of the concrete for 10% substitution with WCTA, while it leads to a decrease in water absorption for 20- 50% substitution with WCTA, with 30% having the least water absorption. Therefore it is recommended to limit the replacement of granite with WCTA to a maximum of 40%, while for optimal strength and durability of structural concrete, replacement of granite with WCTA should be kept at 30%.