Cement production has a lot of adverse effects on the environment and the globe at large. With all these negativities, it becomes imperative to find alternative materials that are sustainable and environmentally friendly to reduce some of these adverse effects. Seashells are one of the numerous wastes that are quickly accumulating onshore coasts. Using seashells in cement aids in ridding seashells from seashores and landfills, and transforming these wastes to viable cementitious materials. This review paper summarizes past studies on using seashell ash powder as a partial replacement for cement in several proportions. The workability of concrete reduces with the addition of seashell ash. It also indicates a reduction in compressive strength of concrete whose cement content is partially replaced with seashells as compared to those of ordinary Portland cement (OPC). Also, at low percentages of 5%-15% ranges, the concrete absorption and porosity are less compared to standard. Though, with greater replacement levels of up to 25%-50%, these values are enhanced. The workability of concrete is reduced with the addition of higher percentage of seashell ash. After long curing periods, concrete permeability is also reduced, and the mechanical performance is enhanced.

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Applications of agricultural by-product as substitute for non-renewable material in cement production are desirable in stimulating socio-economic development. In this study, Rice Husk Ash (RHA) blended cement was produced by replacing 5%, 7%, 11.25%, 15%, 20.25% and 25% by weight of Ordinary Portland Cement (OPC) clinker with RHA. The cement without RHA serves as the control. The chemical compositions of RHA, OPC-clinker and the blended cements were determined using X-ray fluorescence analyzer. The physical characteristics of RHA blended cements that were considered are fineness, soundness, consistency, initial and final setting times and compressive strength at 2, 7, 28, 56 and 90 curing ages. The results showed that RHA is a suitable material for use as a pozzolan as it satisfied the minimum requirement by having the sum of SiO2, Al2O3 and Fe2O3 of more than 70%. Incorporation of RHA led to an increase in the composition of SiO2 and reduction in that of CaO. An increase in RHA content showed a decrease in compressive strength at early ages and slightly increase at a later age (90 days). The blended cement produced with lower levels of RHA replacement conforms to standard specifications specified in BS EN 197-1:2000, NIS 439:2000 and ASTM C 150-02. The minimum Strength Activated Index (SAI) of 75% at the age of 28 days of curing as specified by ASTM C 618 was satisfied by RHA replacement of up to 15%. It was concluded that blended cement with the maximum of 15% RHA content is suitable for use for structural purposes.

The rate at which the construction industry explores and consumes non-renewable natural aggregates and other industrial products such as bitumen, lime, and cement during construction and rehabilitation of road pavements has over time proven to be environmentally degrading and non-sustainable. This, alongside the issues of high solid waste generation and inadequate disposal, has led to series of studies by various researchers to find methods to integrate these solid wastes as alternative materials in road construction and maintenance. This paper provides a simple yet detailed review of recent relevant studies conducted to understand the alarming rate of generation and the effects of reusing these waste materials in both flexible and rigid pavements. The review further outlines the advantages and disadvantages of the selected waste materials and compare the results with that of conventional materials in accordance with relevant standards while highlighting the performance, and life cycle environmental and economic sustainability implications. The study shows that the adoption of these materials offers efficiency in waste disposal while reducing the demand for natural aggregates and consequently, significantly reducing life cycle impacts and costs. The challenges limiting the effective practical implementation of these waste recycling techniques in the construction industry were discussed and possible solutions were suggested to encourage and ensure its utilization in road construction.

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