Opportunity for increasing the soil quality of non-arable and depleted soils in South Africa: A review

The improvement of food security strategies on highly degraded soils has become a major challenge for South Africa, as the need to secure food sources for the growing population under harsher climatic conditions. South Africa is one of the many water scarce countries and is label 30th driest country in the world. The ability of a soil to serve as a growth medium for plants is directly influenced by the chemical, physical, and biological parameters but most importantly the fertility of the soil, which is a prominent part of soil quality. Numerous methods exist to enhance and maintain soil quality including the application of fertilizers and the other includes the application of geological materials to the soil. Basalt (commonly referred to as rock dust) application as a soil amendment has been the focus of numerous long-term studies on soil fertility. The results of long-term application of rock dust have indicated a reduction in continuously applying additional amendment, resulting in more sustainable farming operations. When considering South Africa's relative scarcity of available agricultural land and harsh climatic conditions against the increasing demand placed on food production by a growing population combined with water scarcity, it becomes evident that it is necessary to search for new innovative methods to improve soil quality, which is deemed non-arable and/or depleted. The potential for basalt in re-mineralisation and application on non-arable soil in South Africa hold enormous benefits for the economy.

Application of Waste Rock Dust in Cement Binding Mixtures Used in Roadway

The article contains the results of research on the effect of waste rock dust on the properties of cement-bound mixtures. Gabbro-limestone dust with a significant proportion of active silica and calcium carbonate was used for the tests. The results of strength tests after 28 days of maturation with a variable proportion of cement (3%, 5%, 7%) and rock dust (0%, 10%, 20%) are presented. The stabilized aggregate was fine sand. The obtained results did not show the expected strength and frost resistance of the tested samples. The analysis of the results shows that the addition of rock dust is not applicable in dusty soils.

Effect of Quarry Rock Dust as a Binder on the Properties of Fly Ash and Slag-Based Geopolymer Concrete Exposed to Ambient and Elevated Temperatures

This study presents the performance of quarry rock dust (QRD) incorporated fly ash (FA) and slag (SG) based geopolymer concretes (QFS-GPC) exposed to ambient and elevated temperatures. A total of five QFS-GPC mix types were prepared. The quantity of FA (50%) was kept constant in all the mixes, and SG was replaced by 5%, 10%, 15%, and 20% of QRD. The fresh, hardened properties of the QFS-GPC mixes, viz., workability, compressive strength, splitting tensile strength, and flexural strengths, and XRD for identification of reaction phases were evaluated. The prepared mixes were also heated up to 800 °C to evaluate the residual compressive strength and weight loss. The workability of the QFS-GPC mixes was observed to be reduced by increasing the dosage (0 to 20%) of QRD. Superplasticizer (SP) was used to maintain the medium standard of workability. The compressive, tensile, and flexural strengths were increased by replacing SG with QRD up to 15%, whereas a further higher dosage (20%) of QRD reduced the mechanical strengths of the QFS-GPC mixes. The strength of the QFS-GPC specimens, heated to elevated temperatures up to 800 °C, was reduced persistently with the increased contents of QRD from 0 to 20%. It was concluded from the study that QFS-GPC can be used to achieve 30 MPa strength of concrete.

Behavior of Quarry Rock Dust, Fly Ash and Slag Based Geopolymer Concrete Columns Reinforced with Steel Fibers under Eccentric Loading

Geopolymer concrete, also known as an earth-friendly concrete, has been under continuous study due to its environmental benefits and a sustainable alternative to conventional concrete construction. The supplies of many source materials, such as fly ash (FA) or slag (SG), to produce geopolymer concrete (GPC) may be limited; however, quarry rock dust (QRD) wastes (limestone, dolomite, or silica powders) formed by crushing rocks appear virtually endless. Although significant experimental research has been carried out on GPC, with a major focus on the mix design development, rheological, durability, and mechanical properties of the GPC mixes; still the information available on the structural behavior of GPC is rather limited. This has implications in extending GPC application from a laboratory-based technology to an at-site product. This study investigates the structural behavior of quarry-rock-dust-incorporated fiber-reinforced GPC columns under concentric and eccentric loading. In this study, a total of 20 columns with 200 mm square cross-section and 1000 mm height were tested. The FA and SG were used as source materials to produce GPC mixtures. The QRD was incorporated as a partial replacement (20%) of SG. The conventional concrete (CC) columns were prepared as the reference specimens. The effect of incorporating quarry rock dust as a replacement of SG, steel fibers, and loading conditions (concentric and eccentric loading) on the structural behavior of GPC columns were studied. The test results revealed that quarry rock dust is an adequate material that can be used as a source material in GPC to manufacture structural concrete members with satisfactory performance. The general performance of the GPC columns incorporating QRD (20%) is observed to be similar to that of GPC columns (without QRD) and CC columns. The addition of steel fibers considerably improves the loading capacity, ductility, and axial load–displacement behavior of the tested columns. The load capacities of fiber-reinforced GPC columns were about 5–7% greater in comparison to the CC columns. The spalling of concrete cover at failure was detected in all plain GPC columns, whereas the failure mode of all fiber-reinforced GPC columns is characterized with surface cracking leading to disintegration of concrete cover.