Abstract: This paper presents the results of the laboratory evaluation of the characteristics of lateritic soil stabilized reclaimed asphalt pavements (RAP), using 0 – 2% cement, subjected to British Standard Light (BSL) compactive effort to determine their index, compaction and california bearing ratio (CBR) results. The result of the laboratory tests show that the properties of RAP improved when stabilized with lateritic soil, using up to 2% cement. The particle size distribution improved from poorly graded sandy GRAVELLY material for 100% lateritic soil and very sandy GRAVELLY material, to the gradation described as well graded very sandy GRAVELLY material for lateritic soil stabilized RAP, using up to 2% cement. The CBR results obtained from the study show that using the Nigerian General Specifications, 180% CBR value criterion, the maximum CBR of 55% (soaked) for the mix proportion; 40% Laterite + 58% RAP + 2% Cement for A-2-7(2) soil prescribed by the latter is not adequate for stabilization of base coarse. However, judging by the 24-hour strength gain from 17.9 (unsoaked) to 55% (soaked) CBR values, the material can be used as subgrade and subbase materials.
Abstract: This paper presents the mechanical properties of sawdust concrete and its application as criteria for rigid pavement works. Sawdust concrete with nominal mixes 1:1:2, 1:1½:3, 1:2:4, 1:3:6, and 1:4:8 (1 part cement to 1, 1½, 2, 3 or 4 parts fine sand to 2, 3, 4, 6 or 8 parts sawdust) with 0.60 water-cement ratio were produced and cast into cubes, beams and cylindrical shape for the compressive, flexural and split tensile strength tests, modulus of elasticity and Poisson’s ratio tests. The derived values were compared with the Nigerian and British Ports Association standards/codes for rigid pavements. The slump values for all fresh mixes ranged between 0.10-0.20mm which indicated low workability, while their strength increased with maturity. Only nominal concrete mixes 1:1:2 and 1:1½:3 possessed adequate compressive and flexural strengths for rigid pavement works. Hence, they were recommended as sawdust concrete rigid pavement surfacing, cement bounded base or sub-base materials.
Abstract: This paper presents the results of a laboratory study on the effect of oil contamination on the particle size distribution and plasticity characteristics of lateritic soil. The soil was artificially contaminated with a maximum 6 % oil content by weight of dry soil. The results show that there was a substantial reduction in the amount of fines content with higher amounts of oil in the soil matrix. The percentage of fine fraction in the natural soil was 86.9 % and on contamination with maximum 6 % oil content by weight of dry soil at optimum moisture content (OMC) the fine fraction reduced to 1.4 %. The plasticity index decreased from 16.0 to 8.5 % when contaminated with 6 % oil content by weight of dry soil. The plasticity modulus (PM), plasticity product (PP), the shrinkage modulus (SM) and the grading modulus (GM) decreased with increasing amounts of oil content.
Abstract: Large quantities of oil contaminated soils result from pipeline vandalization, onshore and offshore oil spills every year in Nigeria. An extensive laboratory program was carried out to determine the effect of varying compactive efforts on the hydraulic conductivity behaviour of oil contamination lateritic soils. Hydraulic conductivity tests were carried out on both the natural and oil contaminated soil samples at the Reduced British Standard Light (RBSL), British Standard Light (BSL), West African Standard (WAS) and British Standard Heavy (BSH) compaction energies. Contaminated specimens were prepared by mixing the lateritic soil with maximum 6 % oil concentration by weight of dry soil. The results obtained indicated a decrease in the hydraulic conductivity of the contaminated soil samples with increasing compactive efforts.
Abstract: The paper examined the cost benefit of optimized five-component-concrete mix. Mound Soil randomly selected from Iyeke-Ogba in Benin City was used as a case study of a fifth component in the concrete mix. The work applied Scheffe’s optimization technique to obtain concrete mix proportions. A mathematical model for the optimizing concrete of five components namely; cement, fine aggregate, mound soil, coarse aggregates and water/cement (w/c) ratio, was developed. Cube samples measuring 150mm x 150mm x 150mm were made with the developed mixes and compared with the results of a standard 1:2:4 mix. The samples were tested at 7, 14 and 28 days for compressive strength. The costs of producing a unit volume of the concretes were determined and compared. The results showed that the standard mix gave a 28th day maximum strength of at a w/c of 0.5 and the theoretically optimized design mix gave a mix proportion of 1.00:1.59:0.46:3.34:0.53 and a compressive strength of. This mix was tested experimentally and it gave, representing an increase of 15.33%. The cost benefit analysis showed that Scheffe’s optimized mound soil concrete, MSC was 15% more economical than the standard mix plain concrete.
Abstract: Accidental or deliberate operational discharges of organic chemicals or wastes containing organic chemicals induce geochemical reactions with resultant adverse effects on basic geotechnical properties of the soil. To utilize soil materials from such sites for engineering construction or as foundation soil, stabilization must be carried out. In this study, cement kiln dust (CKD) was applied to lateritic soil contaminated with three different types of commonly occurring organic chemicals namely benzene, ethanol and kerosene to evaluate the restoration and improvements in the engineering properties. Contamination was simulated in the laboratory by adding known quantities (2.5, 5, 7.5 and 10%) of each of the chemicals separately to lateritic soil samples and allowed to air dry for 14 days before stabilizing with 10% CKD. Performance was evaluated on Atterberg limits, compaction characteristics, strength properties and hydraulic conductivity of the contaminated soil. Strength and hydraulic conductivity specimens were compacted with British Standard Light (BSL) compactive effort at predetermined optimum moisture content. Results showed that the simultaneous effects of the cementing and pozzolanic action of the CKD rejuvenated the geotechnical properties of the soil, in most cases comparable to the properties at the original pristine condition. Studies on durability and long term competent performance of the stabilized contaminated soil specimens is in progress.
Abstract: Concrete is an excellent structural material and considered as essential for the modern civilization and human society. Now, use of waste tyres in concrete has become technically feasible and the concrete is being considered as light weight concrete. The composites were formed with 0%, 5%, 10%, 15%, 20% and 25% of fibers replaced by coarse aggregate weight. The fibers were of different lengths (L) such as 25mm, 50mm and 75mm had holes of diameters (D) 4mm, 5mm and 6mm. The holes functioned as anchors in the cement matrix so that the tyre fibres shall not be separated while placing in the mould. The 3rd, 7th and 28th day’s compression strength and crack patterns were observed on cubes. Split tensile strength on 14th and 28th day were tested on cylindrical specimens. Test results have shown that the increase in rubber content decreases the compressive strength, but, increases the strain energy while conducting the split tensile tests. The composite with fiber specimen L50-D5 and L50-D6 with 10% replacement of coarse aggregate had shown better results than other specimens. However, further studies are needed to reveal the hidden properties of tyre fiber modified concrete.
Abstract: This study was carried out as an investigation into concrete products as an appropriate alternative for plastic, rubble stone and steel in the construction of domestic water tanks, door and window frames in the Rwandan construction industry. This project is an innovation aimed at adding value to the available resources of materials and personnel to expose untapped opportunities that are beneficial to the Rwandan community and the world in general through conservation of the environment and creation of employment. In a similar sense, this effort responds to the result of too much consumption of wood products in this rapidly growing infrastructure sector and calls for alternatives such as concrete in construction of door and window frames .In order to answer the research objectives, the researchers opted to observe, carry out demonstrations/ modeling, views of the end users of the product especially for water tanks. Data gathered from this research instrument were then computed and interpreted. Along with primary data, the researchers also made use of secondary resources in the form of published articles and literatures to support the survey results. Curved interlocking concrete blocks are affordable, environment friendly, labour intensive and use locally available materials, adoptable by both the rural and urban settings, uses local materials and uses local labour hence providing employment. At the end, these products were compared with conventional materials for their costs and maintenance. The results show promise as new construction material suitable for use in Rwanda. However, use of concrete for door and window frames is new to Rwanda and should further be investigated for adoptability.
Abstract: Laboratory study on compacted tropical clay treated with up to 16% rice husk ash (RHA), an agro-industrial waste; to evaluate its hydraulic properties and hence its suitability in waste containment systems was carried out. Soil-RHA mixtures were compacted using standard Proctor, West African Standard and modified Proctor efforts at-2, 0, 2 and 4% of optimum moisture content (OMC). Compacted samples were permeated and the hydraulic behaviour of the material was examined considering the effects of moulding water content, water content relative to optimum, dry density and RHA contents. Results showed decreasing hydraulic conductivity with increasing moulding water content and compactive efforts; it also varied greatly between the dry and wet side of optimum decreasing towards the wet side. Hydraulic conductivity generally decreased with increased dry density for all effort. Hydraulic conductivity increased with rice husk ash treatment at the OMC; but were within recommended values of 1 x 10-7 cm/s for up to 8% rice husk ash treatment irrespective of the compactive effort used. This shows the suitability of the material as a hydraulic barrier in waste containment systems for up to 8% rice husk ash treatment and beneficial reuse of this agro-industrial waste product.