The study utilized two locally abundant materials; Cassava Peels Ash (CPA) and Laterite as constituents for rural projects. The availability of these materials in West-Africa permitted the study. Partly blending Ordinary Portland Cement (OPC) and Sand with an agricultural waste-CPA and Laterite respectively against the effect of short-term hydration on the products compressive strength were investigated. 192 cubic specimens of 100 mm dimensions were cast and cured in water for 7, 14, 21, and 28 days, adopting a control of 28 day-25 N/mm2 targeted strength. The OPC/CPA and sand/laterite substitute ratios were 0-30% with views to determine the best substitute matrix. Density and compressive strength decreased with increased CPA and laterite content. However, strength development increased over hydration ages. 28 days density and compressive strength of the normal concrete were 2385 kg/m3 and 27.05 N/mm2 while the best matrix (10% CPA+10% laterite) had 2322 kg/m3 and 25.57 N/mm2 respectively. The strength of the green concrete was higher than the adopted strength at 28 days, which makes it suitable for use. It can be used without compromising standards in simple foundations and masonry units as a prime cost reduction in rural housing and development.

The environmental impact of cement and concrete can be significantly decreased by the reduction of the amount of Portland cement clinker. The substitution of the Portland cement clinker with substitutes like limestone powder results in a decrease of hydration products, such as calcium hydroxide. However, a minimum amount of calcium hydroxide and a high density of the hardened cement pastes are necessary to ensure sufficient alkalinity, which is necessary for the passivation of the steel reinforcement during the life cycle of a building. The development of new eco-friendly cements requires a basic understanding regarding the durability against carbonation induced corrosion of the reinforcement. We are investigating low-water limestone-rich concretes with the aim for a sufficient prediction of the carbonation resistance and hope to support the development of sustainable cements. Because of the low content of hydration products, the approved models describing the carbonation behavior of conventional concretes are not working sufficiently for the mixtures investigated here and therefore, need to be modified. For that reason, the individual phase-pure clinker phases were synthesized and after complete hydration stored under CO2 atmosphere (2 Vol %, 20 A°C, 65% humidity) for 28 days. The products of the hydration- and carbonation-reactions were investigated with X-ray powder diffraction, thermal analysis (DTA/TG), scanning electron microscopy and energy-dispersive X-ray analysis. The results are compared to analyses of conventional clinker phases.

Worldwide cement production is a high energy consuming industry; 90% is thermal and 10% is electrical energy. This is the third most anthropogenic related carbon dioxide emitting industry in the world. With a rising price of energy and a growing emphasis on environmental issues, the cement industry is facing significant challenges to remain both competitive and sustainable. Composite cement manufacturing is one alternative that is used to reduce energy use and greenhouse gas emissions. The dry grinding process used for finished product represents 40-50% of electrical energy consumption. It is a very inefficient process generally ranging around 1% efficiency.
This research evaluated the process of a typical Portland cement grinding circuit in order to identify inefficiencies in the process and how the operating parameters may be changed in order to improve the system's performance. Tests were conducted using samples from a B.C. cement producer and the results were analyzed in order to characterize and build a high accuracy model that can be used as a bench marking tool. Representative sampling and mass balance were performed on the circuit using real steady state operative conditions data provided by process plant managers.

Major research findings are:
• Air separator efficiency is rated 46.06% efficiency at fractions below 35 microns.
• High dust load feed and agglomeration are the main reasons for this low separator efficiency.
• Agglomeration effect is related to overgrinding, high energy impacts and the use of limestone.
• Whiten model is an adequate tool to fit and correct experimental data on cement air separators and to provide quantification of operating factors to evaluate the separation process.
• Low grinding kinetics at ball mill compartment 01 suggests improper size grinding media selection and high wear rate for the case studied (for media and liners).

The cement industry faces a number of challenges that include depleting fossil fuel reserves, scarcity of raw materials, perpetually increasing demand for cements and concretes, growing environmental concerns linked to climate change and an ailing world economy. Every tonne of Ordinary Portland Cement (OPC) that is produced releases on average a similar amount of CO2 into the atmosphere, or in total roughly 6% of all man-made carbon emissions. Improved production methods and formulations that reduce or eliminate CO2 emissions from the cement manufacturing process are thus high on the agenda. Emission reduction is also needed to counter the impacts on product cost of new regulations, green taxes and escalating fuel prices. In this regard, locally available minerals, recycled materials and (industry, agriculture and domestic) waste may be suitable for blending with OPC as substitute, or in some cases replacement, binders. Fly ash, Blast furnace slag and silica fumes are three well known examples of cement replacement materials that are in use today that, like OPC, have been documented and validated both in laboratory tests and in practice. The first is a by-product of coal combustion, the second of iron smelting and the third of electric arc furnace production of elemental silicon or ferro silicon alloys. This paper presents a concise review of the current state-of-the-art and standards underpinning the production and use of OPC-based cements and concretes. It outlines some of the emerging green alternatives and the benefits they offer. Many of these alternatives rely on technological advances that include energy-efficient, low carbon production methods, novel cement formulations, geopolymers, carbon negative cements and novel concrete products. Finally, the economics of cement production and the trends in the GAMBIA and AFRICA Region are presented, to help guide and inform future developments in cement production based on maximizing the value of carbon reduction

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