Concrete bricks and blocks are widely used in South Africa due to their availability, affordability, and durability. However, their production depends heavily on natural aggregates, contributing to resource depletion, landfill pressure, and about 5 million tons of CO2 emissions annually [1]. As natural sources become increasingly constrained, alternative aggregates such as recycled construction and demolition waste (C DW) and gold mine tailings (GMT) are being explored for sustainable brick and block production. This paper reviews current evidence on the performance, environmental impact, adoption potential, and policy considerations surrounding the use of C DW and GMT in South African masonry applications. While both materials demonstrate technical viability, C DW emerges as the more practical and immediately scalable option due to its higher compressive strengths, lower processing costs, and active use in urban centres. However, adoption remains limited by the absence of national standards, inconsistent waste quality, and a lack of formal policy support. Recycled C DW aggregates offer a feasible, climate-aligned solution for producing non-structural concrete bricks and blocks in South Africa. To enable broader adoption, the development of quality control guidelines, region-specific lifecycle assessments, and revisions to regulatory frameworks are recommended.

Construction and demolition waste (CDW) is defined as non-hazardous waste produced during the construction, repair and rehabilitation, or demolition of infrastructure. While only 16

The South African Oxygen Permeability Index test (OPI) and Swiss Torrent air permeability test (TPT) are well-established methods used for gas permeability evaluations of concrete infrastructure. Comprehensive laboratory experiments have shown the compatibility of the two methods as a combined approach for enhancing the durability assessment of the concrete cover layer. However, this synergy has yet to be investigated under ambient conditions. This paper explores the practicality of an integrated method using the OPI and TPT methods together. Concrete panels were manufactured and exposed to ambient conditions in Cape Town, South Africa. Gas permeability tests were carried out at 28 and 56 days to observe the responsiveness of the OPI and TPT to variables such as water/binder ratio (w/b), binder type, and age. The results indicate that the two methods correlate reasonably well with existing data in dry site conditions. However, further investigations are warranted to understand the influence of moisture on the correlation between the TPT and OPI in moist conditions. This work suggests an approach to implement a combined methodology for gas permeability assessment. The approach provides insights into the benefits of combining non-destructive and destructive methods to enhance the durability evaluation of concrete.

This book provides a detailed guide to the selection and use of aggregates in concrete. It presents an overview of aggregate sources and production techniques, followed by a detailed study of their physical, mechanical and chemical properties. Then it looks at the use of aggregates in both plastic and hardened concretes, and in the overall mix design. Special aggregates and their applications are discussed, as are the current main specifications, standards and tests.

The surge in population and urbanization in South Africa has increased construction activities, leading to the generation of a significant amount of construction and demolition waste (C DW). While a portion of this waste is used in low-grade applications, the rest ends up in landfills. The conventional use of virgin materials persists, contributing to environmental issues such as increased energy usage and CO2 emissions from the mining and transportation of raw materials and the use of cement in concrete production. To promote a circular economy, resource efficiency, and reduced carbon footprint, a shift toward C DW recycling is imperative. Despite successful international practices, the recycling rate in South Africa still needs to improve. While previous research works have focused mainly on using recycled aggregates (RAs) in structural concrete, this review explores their potential use in the manufacturing of low-strength concrete bricks and blocks, which are essential construction products within the context of housing development in South Africa. The lack of certification and standards for RAs in South Africa has hindered their practical use. Thus, different stakeholders need to take responsibility for investigating and developing quality control procedures to ensure consistency.

This study investigates the potential use of the non-destructive Wenner resistivity method and the chloride conductivity method in quality assessment, and in estimating input parameters for service life modelling, of concrete. The experimental investigation was conducted on plain Portland cement, fly ash and slag concretes with a range of cement replacement levels and w/b ratios. The results of this study showed that the use of Wenner resistivity to assess the ionic transport resistance without regard to the pore solution chemistry can lead to misinterpretations. This effect was especially noticeable in fly ash concretes. Similarly, penetrability evaluation by the Wenner method in air-dried specimens requires considerations of saturation effects even after prolonged wetting. The chloride conductivity test showed more reliability against the effects of the pore solution chemistry and degree of saturation. This study also highlights the importance of considering the long-term evolution of concrete penetrability in relation to the environmental conditions. In this regard, the Wenner method was very useful in the characterisation of the time-dependence of the resistance to chloride transport of concrete under saturated conditions. A promising application of this finding is in service life modelling for reinforced concrete structures under marine conditions.

This study investigated the physical, chemical and mineralogical properties of fine recycled aggregate (FRA) and their influence on the properties of fresh and hardened concrete. Four FRA fractions, obtained from a single source of parent concrete, were investigated separately to determine the effect of particle size on FRA properties. These were compared to two common South African fine natural aggregates (FNA) - dune sand and greywacke crusher sand. The parent concrete was characterised by compressive strength and carbonation measurements, while water absorption, density, particle size analysis, X-ray fluorescence (XRF), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) were carried out on the fine aggregates and cement. While the FRA displayed less dense and porous adhered cement paste (ACP), as expected, the ACP consisted largely of hydrated cement phases which were more concentrated in the finer (<0.15 mm) powder fractions. The results inferred that, for new concrete applications incorporating the FRA, phases in the ACP such as Ca(OH)2 and C-S-H react with CO2 during the carbonation of concrete to produce a buffering effect, while the C-S-H assists in chloride binding. This is in addition to the capacity of calcite, C-S-H and AFt in the ACP to provide nucleation sites, thereby promoting hydration reactions in new concrete. Furthermore, the properties of the ACP can be optimised through synergistic reactivity between the chemical phases in the binder and the ACP to improve the long-term mechanical and durability performance of new concrete.

Construction and demolition waste (CDW) is defined as non-hazardous waste produced during the construction, repair and rehabilitation, or demolition of infrastructure. While only 19

This paper discusses the performance of calcium sulpho-aluminate (CSA) cement and a Sulphate-Resisting Portland Cement (SRPC) with a fly ash (FA) additive (i.e., a SRPC + FA binder system) in a ‘live’ sewer environment; it deepens the understanding of their deterioration mechanisms by using a laboratory test for simulated sewer conditions. It also studies the role of an iron-based additive (‘Hard-Cem®’, HC) in improving the performance of SRPC + FA concrete under a biogenic acid attack. The performance of 0.4 w/b concrete specimens of the three binders (CSA, SRPC + FA, and SRPC + FA + HC) with calcite aggregates in sewer exposure was assessed by visual observation, measurements of mass and thickness changes, and microstructural analysis for approximately 25 months. The laboratory test, i.e., the Biogenic Acid Concrete (BAC) test, was used to study the deterioration mechanisms of these binders in terms of leaching solution pH and standardised cumulative leached calcium and aluminium. The results indicate that CSA concrete had improved performance in the sewer environment, showing no mass loss and only about one-third of thickness lost in the SRPC + FA concrete over a 25-month exposure period in the sewer environment. The BAC test results complemented the field observations. The iron-based additive in sewer concrete slightly reduced mass loss, likely due to its better resistance to abrasion and erosion, but not due to any chemical influence, since it does not participate in hydration or dissolution reactions. The findings imply that CSA cement may represent a suitable alternative binder for concrete sewer construction. They also suggest that a surface hardener has limited benefits, except when it is under abrasive conditions. Further investigation is required, especially since CSA contains high amounts of sulphate, the effect of which is not well understood.

Concrete sewer surfaces made with Portland Cement (PC) consistently exhibit deterioration products such as gypsum and amorphous silica, despite relatively high measured in-situ concrete surface pH values (typically 4–2) in relation to the lower expected pH of the attacking acid. This is because the alkalinity of concrete neutralises the sulphuric acid produced by Sulphur-Oxidising Bacteria (SOB), masking the true acidity at the surface. Consequently, the actual pH driving corrosion is problematic to measure directly, yet it is hypothesised to be as low as pH 1. This study investigates the corrosion mechanisms of PC binders under controlled sulphuric acid attack at pH 1, 2, and 4 using a laboratory titration method coupled with reactive transport modelling, and microstructural analyses, i.e., X-ray diffraction (XRD), Scanning Electron Microscopy (SEM), and Quantitative Evaluation of Minerals by SEM (QEMSCAN). Results show that at pH 1, the most aggressive condition, gypsum and amorphous silica concentrations were highest, with their content decreasing as pH increased. Reactive transport modelling confirmed that reduced availability of SO₄2⁻ and H⁺ ions at pH > 1 limits gypsum formation, implying that SOB must generate acid close to or below pH 1 to account for the observed gypsum formation (and associated surface zonation) on the exposed surface. The significance of this study lies in bridging laboratory, modelling, and field observations to advance understanding of biogenic sulphuric acid corrosion. These insights improve the accuracy of durability predictions and support the development of effective mitigation strategies for concrete sewer infrastructure.

This study investigated the effect of replacing natural dune sand with fine recycled concrete aggregates (fRCA) produced using real concrete construction and demolition waste (CDW) and with a maximum particle size of 1.18 mm on the fresh and hardened properties of concrete. Concrete with w/b ratios of 0.45 and 0.60 was produced. Natural fine aggregates comprised of a 50/50 mix of dune sand and crusher dust. fRCA replaced the dune sand portion of the natural fine aggregates by 0

This paper focuses on concrete degradation of hydraulic conveyance components of a hydropower project in Uganda that was commissioned in 2019. During a routine outage inspection in 2021, concrete damage was observed in the waterways. The engineering-procure-construct (EPC) contractor was notified to remedy the defects but they declined, claiming that it was normal erosion wear. In order to ascertain the root cause, avert a potential dispute, and apportion liability, a forensic investigation was conducted by the owner. Site inspections, water quality sampling and testing, and concrete core sampling and testing were carried out during the forensic investigation. The findings indicate that the Nile River water is highly aggressive, and the coupled soft water attack and hydraulic erosion-abrasion led to the premature concrete surface degradation. In order to enhance durability and long-term performance of the waterways, a protective surface coating has been recommended. The investigations have been very useful to avert costly and time-consuming disputes between the owner and the contractor because the cause and party responsible for the defects have been identified, and the contractor has agreed to take remedial action in accordance with the contract. The study will be useful for other planned hydropower projects along the Nile River and similar projects globally. The paper reveals the significance of forensic investigations at a hydropower infrastructure project to ascertain the durability of the civil engineering components of the facility, and in turn the overall performance of the infrastructure. The study undertakes a forensic investigation of concrete degradation within hydraulic conveyance components of a recently commissioned hydropower project in Uganda. The findings reveal practical insights for industry practitioners on the key design and construction considerations for hydropower plants or similar water conveyance systems. Key findings from the investigations, as well as durability recommendations for future project waterways, are shared for best industry practice, including adopting a comprehensive durability design and performance-based approach for key infrastructure such as hydropower plants.

Africa is one of the regions where significant construction will be experienced in future. While the use of Limestone Calcined Clay Cement (LC 3 ) is considered a viable option for lowering costs and environmental impact of concrete, its viability needs to be verified based on performance assessment of locally available constituent materials. In this study, the performance of LC 3 mixes with clinker contents of 45 %, 55 %, and 65 % with four different clays from South Africa and Tanzania, was assessed and compared with two conventional concrete mixes. Overall, it was concluded that, LC 3 mixes are characterised by reduced penetrability, increased electrical resistivity, higher chloride ingress resistance, and increased carbonation rates, indicating superior durability performance for marine exposure conditions. Factors such as the specific surface area of the clay and the alkali contents were found to influence the performance of the system, and these aspects require further study to better understand their influence.

Population growth coupled with rapid urbanisation have produced a continued increase in construction and related demolition activities for projects such as housing developments, commercial buildings, and public infrastructure, especially in developing countries in the Global South. The deposition of construction and demolition waste (CDW) into landfills depletes land resources, potentially poses environmental hazards and results in disposal of potentially useful resources that can be used to produce concrete according to circular economy principles. Joint research activities at the Universities of Cape Town and the Witwatersrand in South Africa and IIT Madras in India have resulted in the development of a monograph on recycled concrete aggregates and their influence on concrete properties. The monograph and associated online teaching material, published in 2023, aim at informing industry and academia about current challenges and opportunities in the fields of CDW generation and management and concrete manufacture with recycled concrete aggregate (RCA). The background to the monograph is presented together with an overview on the generation of RCA and recent results on the durability of RCA concrete.

This paper seeks to provide a better understanding of the performance of calcium sulfoaluminate cement (CSA) in comparison with calcium aluminate cement (CAC) and Portland-limestone cement, CEM II A/L 52.5 N (CEM II) in live sewer environments, thereby providing rich field data for enhancing sewer concrete design. Three concrete mixes using these binders, with 0.34 w/b, siliceous pit sand, and dolomite aggregates, were prepared and exposed for 26 months in two sewer sites. Visual observations, measurements of concrete surface pH, and mass and thickness change were conducted regularly to observe deterioration. After exposure, microstructural analyses based on SEM, QEMSCAN, and XRD were conducted to clarify the deterioration mechanisms further. Regardless of sewer exposure conditions, the results indicated that CAC concrete had superior performance, followed by CSA, then CEM II. Sewer hydraulic action and high H2S gas concentrations (max. > 300 ppm) caused accelerated corrosion rates. Binder performances were primarily related to their chemistry, mineralogy, and aggregate interaction.

The service life of a sewer is often set at around 100 years, regarded as a sufficient operational period without significant repairs being required. However, sewer concrete may experience severe deterioration, leading to structural and functional failures. 40

Carbonation-induced reinforced steel concrete corrosion is a prominent concern related to engineering design and maintenance. The Durability Index (DI) approach was developed in South Africa to address this concern and enhance the durability performance of reinforced concrete structures. This approach relies on durability index tests, which are associated with transport mechanisms linked to specific deterioration processes. The carbonation of concrete is primarily influenced by the microstructure and transport characteristics of the concrete. Environmental exposure conditions also influence the rate of carbonation. The focus of the research reported here was to develop a carbonation model that could predict the rate of carbonation of concrete exposed to, or sheltered from, rain, with the permeability coefficient (k) from the Oxygen Permeability Index (OPI) test (DI test) as the key unifying variable. The model development was based on natural carbonation data and the drying profiles (experimentally measured) of 48 different concretes. Concrete microstructure was varied by varying the water-to-cement ratio, curing conditions, and by using SCMs. The resulting carbonation model was able to predict the rate of carbonation of concrete, allowing for different exposure conditions. A unique feature of this model is its use of a single material property, the 'k' value, to effectively address both CO2 diffusion and the drying process within concrete. The model displayed sensitivity towards the influence of variation in CO2 concentration, concrete microstructure, and the environmental exposure conditions, making this a simplified, effective and practical concrete carbonation prediction model.