Investigations of the structural characteristics of concrete produced from recycled aggregates at varying water/cement ratios

The paper tried to investigate the structural characteristics of concrete produced by partially replacing natural aggregates with recycled aggregates at varying water/cement ratios. The study is basically a laboratory experimental study. Water/cement ratio component of the concrete were varied at 0.40, 0.45, 0.50, 0.55, 0.60; while the natural aggregate was partially replaced with RCA of 0%, 15%, 30%, 45%, 60%, 75% and 90% for concrete productions for 7, 14 and 28 days structural characteristics. The densities, water absorption capacity and Compressive Strength of these concretes were determined. The results were presented in graphs and Tables. Results of the study indicate an increased compressive strength at low percentage of RCA and water /cement ratio values. There is a marginal difference between compressive strength of normal concrete and concrete produced by partial RCA of 15% replacement at 0.4 w/c ratio. Keywords: recycled concrete aggregate, natural aggregate, compressive strength, water/ cement ratio and natural aggregate concrete

Regression modeling of the strength properties of concrete reinforced with polypropylene fiber and alkali resistant glass fibre

This paper presents the result of the regression modeling of the strength properties of hybrid fiber reinforced concrete made with polypropylene fiber (PPF) and alkali resistant glass fibre (ARGF). The fibres were added to grade 25 concrete at different proportion of 0.5%, 1.0%, 1.5% and 2.0% of volume of concrete. A total of sixty three cubes samples were tested for compressive strength, twenty four cylindrical samples for split tensile strength and twenty four beam samples for flexural strength. Maximum compressive strength was attained at 1.5% fibre volume with hybrid fibre ratio of 80% ARGF and 20% PPF, maximum split tensile strength was attained at 1.0% fibre volume with hybrid fibre ratio of 80% ARGF and 20% PPF. The beam samples attained its maximum flexural strength at 1.0% fibre volume with hybrid fibre ratio of 60% ARGF and 40% PPF. Empirical expressions were established by using multiple regression analysis to predict the compressive, split tensile and flexural strengths of the hybrid fibre reinforced concrete made with PPF and ARGF. The predicted values compared favourably with the experimental results from all specimens.Keywords: alkali resistant glass fibre, compressive strength, flexural strength, hybrid fibre concrete, polypropylene fibre, regression modeling. reinforced concrete, split tensile strengt

Predictive model for compressive strength of concrete made from recycled concrete coarse aggregates

The objective of the study is to replace coarse natural aggregate with recycled concrete coarse aggregate (RCCA) for concrete production in order to determine the compressive strength of such concrete for different percentages of partial replacement using different water/cement ratios. Thereafter develop a predictive model for the compressive strength using different percentages of partial replacement and water/cement ratios. The polynomial regression model was applied to examine the correlation between the compressive strength of concrete, water cement ratio and %RCCA. The following regression models were established for 28 days at 0.4, 0.45 and 0.50 water cement ratio,f28,0.4 = -0.000(%RCCA)²- 0.192(%RCCA) + 49.79 with R² = 1,f28.0.45 = 0.000(%RCA )² - 0.371(%RCCA) + 44.29 with R² = 1, and f28,0.50 = -0.001(%RCCA)² - 0.386(%RCA) + 41.91 with R² = 1. At 28days test for water cement ratios of 0.55, 0.6 and 0.65 as f28,0.55 = -0.0001(%RCCA)² - 0.158(%RCCA ) + 38.26 with coefficient of determination of R² = 1, f28,0.60 = 0.010(%RCCA )² - 0.1954 (%RCCA) + 28.29 with R² = 1, while for W/C ratio of 0.65 is given as f28,0.65= -0.001(%RCCA )² + 0.222(%RCCA) + 18.37 with coefficient of determination, R² = 1. It was concluded that the increase or decrease in compressive strength of concrete was dependent on percentage replacement ratio of natural aggregate to recycled concrete aggregate (%RCCA) and the amount of water to cement ratio (w/c) ratio of the mix. The significance of the study is that the compressive strength of concrete made with RCCA which is a waste product can be predicted by using the predictive model developed.Keywords: Concrete, Compressive strength, natural aggregate, Predictive model,Recycled concrete aggregate, Water/ cement ratio

The effect of sugar cane juice on setting times of various types of cement produced in Nigeria

The objective of this research is to investigate the influence of Sugar Cane Juice (SCJ) on the setting times of various cement pastes. Sugar Cane Juice is incorporated with four different types of cement brands commonly found in Nigeria. The test results revealed that under normal curing conditions (Temperature=220C) and Relative Humidity = 60%), the efficiency of SCJ in retarding all four types of cement setting increases with increasing SCJ content. For three out of the four brands of cement, the initial setting times remained constant between 0 and 5%., After 5% SCJ content, the initial setting time increased as the SCJ content was increased. For the EAGLE cement brand, the initial setting and final setting times, remained constant between 0 and 3% SCJ content. The final setting times for the UNICEM, IBETO and EAGLE cement remained constant at between 0 and 5% SCJ content. Thereafter, the final setting time increased as the SCJ content increased. The final setting time for the DANGOTE cement experienced an increase immediately after the 0% SCJ content.Keywords: sugar cane juice, setting time, cement past

Partial replacement of coarse aggregate with crushed ceramic tiles in concrete

This paper investigated and reported the improvement of concrete properties by partial replacement of coarse aggregate with crushed waste ceramic tiles (CWCT). Compressive strength tests were conducted using 150x150x1250mm cube specimens. CWCT were used to replace coarse aggregate at 0%, 30%, 40% and 70% replacement levels in the concrete. Compressive strengths at 7, 14 and 28 days curing age was determined at all levels of replacement of coarse aggregate with CWCT. The compressive strength at 7, 14 and 28 days increased as the content of the CWCT was increased between 0%- 30%. At 40% waste ceramic tiles content, the values start to decrease. The optimum replacement value of crushed waste ceramic tile is 30%.Keywords: crushed waste ceramic tiles, coarse aggregate, compressive strength, concret

Potential of Urea Fertilizer (UF) as a retarding admixture in plain concrete

In this study, the use of Urea fertilizer (UF) as a retarding admixture in plain concrete was investigated. Six different mixes of proportion 1:2:4: and a water/cement ratio of 0.5 with (0, 1, 2, 3, 4 and 5%) by weight of urea fertilizer dosage in the concrete mix was adopted. Concrete cubes of 150mmx150mmx150mm made from the mix proportion and dosage of urea fertilizer were cast, cured and tested after 7, 14 and 28 days. It was observed from the study that urea fertilizer acts as a retarder in concrete production. The workability increased as the content of the urea fertilizer in the concrete increased. The compressive strength of the concrete decreased as the content of the urea fertilizer in the concrete increased. The final setting time increased from 20 hours to 50 hours at 5% UF content. The compressive strength decreased by approximately 57% from the control value to the 5% urea fertilizer content. The optimum UF content for standard concrete works is 0.5% which will give a compressive strength of 24 N/mm2Keywords: concrete, compressive strength, retarder, urea fertilizer, workabilit

Exploratory study of crushed coconut shell as partial replacement for fine aggregates in concrete

An exploratory study of crushed coconut shell (CCS) as partial replacement for fine aggregate in concrete was carried out. Mechanical and Physical properties of the CCS and fine aggregate (river sand) were determined and compared. A total of 36 concrete cubes of size 150 x 150 x150mm with mix ratio of 1:2:4 and  water/cement ratio of 0.5 using proportions, 0:100, 25:75, 50:50 and 100:0 CCS  to fine aggregate (river sand) were cast, cured and tested for compressive strength after 14, 21 and 28 days. Compressive strength for 0:100, 25:75, 50:50, and  100:0 CSS: river sand proportions for the 14, 21 and 28 days are (23.85, 24.8, 32.0), (12.29,12.73, 13.80), (15.17, 15.40, 16.44) and (3.23, 3.70, 4.78)  respectively. The trend shows a decrease in strength as the quantity of CCS in the concrete cubes increases. The workability of the concrete decreased as the quantity of CSS increased with the mould slumping at 100% CSS. Aggregate Crushing Value (ACV) for CSS is 8% and that for fine sand is 17.89%,, while Aggregate Impact  Values (AIV) for the CCS is 1.22% and that for river san is 11.8%. Sieve analysis, moisture content, and bulk densities of the CCS, rivers sand and coarse aggregates were also determined. The unit weight of the concrete cubes decreased as the  quantity of the CSS increases in the concrete. The compressive strength of the  50:50 sand: CSS replacement at 28 days for the 1:2:4 mix ratio is 16.44N/mm2. It therefore follows that at 50% CSS replacement, the concrete produced can be used as lightweight concrete. It is estimated that cost reduction of 50% will be achieved.Key Words: crushed coconut shell, concrete, fine aggregate, workability,   compressive strength and slump

Exploratory study of crushed periwinkle shell as partial replacement for fine aggregates in concrete

An exploratory study of crushed periwinkle shell (CPWS) as partial replacement for fine aggregate in concrete was carried out. Mechanical and Physical properties of the CPWS and fine aggregate (river sand) were determined and compared. Concrete cubes of 1:2:4 and 1:3:6 by weight of cement were prepared in the laboratory, using the following proportions, 0:100, 30:70, 50:50 and 100:0 CPWS to fine aggregate (river sand). 14, 21 and 28 days compressive strength test were carried out on the concrete cube. The CPWS had an average moisture content of approximately 11.65%, the highest amongst the aggregates. Physical examination of the CPWS particles showed that the grains were angular in shape with rough surface texture. The sieve analysis test revealed that the particle sizes were fine aggregates with about 98.8% passing through the British sieve No. 4 (4.75mm). The CPWS had a bulk density of 1504kg/m3, while that of the river sand was 1636kg/m3. The workability test revealed that the slump values decreased in the concrete mixture as the quantity of CPWS increased. It was also discovered that the compressive strength decreased with increased percentage of replacement of the river sand with CPWS. The control (highest) 28 days compressive strength of the concrete produced with zero percent CPWS and 100% river sand was 24.89N/mm2. 28 days compressive strength of concrete cubes with 50% CPWS and 50% river sand for mix proportion of 1:2:4 was 18.00N/mm2.From the results of this exploratory study, it can be safely stated that CPWS can be used as a partial replacement of river sand in the production of light weight concrete in areas where the periwinkle shells are in abundance. The purpose of the study is to explore the possibility of turning waste to wealth. A significant factor is that concrete will be produced cheaper in areas with large population of periwinkle shells, while the environment that these periwinkle shells are usually dumped will become better protected.Keywords: periwinkle shell, river sand, coarse aggregate, workability, compressive strength, concret