Mark Alexander

University of Cape Town | UCT · Department of Civil Engineering

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 ass...

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 aggreg...

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 b...

In Africa, one of the most promising options for lowering costs and environmental impact of concrete is the use of limestone calcined clay cement (LC3) systems. However, improper use of the constituent materials may result in a concrete with substandard properties. The results reported here are part of a larger study on the properties of LC3 concre...

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 land...

This paper provides 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. Three concrete mixes using these binders, with 0.34 w/b, siliceous pit sand, and dolomite aggregates, were prepar...

The “Durability Index” (DI) performance-based approach, developed in South Africa, involves the application of early-age concrete test methods together with service life prediction models, and links material properties directly with the expected service life of reinforced concrete (RC) structures under various environmental conditions. The Oxygen P...

This monograph addresses the use of recycled concrete aggregates (RCA) as a replacement for natural aggregates (NA) in concrete applications. It aims to provide information and perspectives on current research trends and gaps as well as to guide practising engineers on the use of RCA in concrete construction and the impact of RCA on the mechanical...

Electrical resistivity measurements are used to assess the potential durability of concrete. The surface resistivity method is a popular method because of the ease of testing, non-destructive nature, and time efficiency. The moisture state of concrete has a significant influence on the resistivity results. Laboratory specimens cured using practical...

Unlike natural aggregate particles, recycled concrete aggregates contain hardened cement paste phases and multiple interfacial transition zones. These differences in properties may be linked to a decrease in durability performance in recycled aggregate concrete. This paper presents a review of the literature published on the durability performance...

This study investigates the chloride penetration resistance of fine recycled aggregate concrete (FRAC). Six concrete mixes comprising 0.45 and 0.55 w/b were prepared using fine recycled aggregates (FRA) at 0, 25 and 50% by volume replacement of natural sand. The chloride penetration resistance of the concrete was tested using the surface electrical...

QEMSCAN (Quantitative Evaluation of Minerals by Scanning Electron Microscopy) was used to analyse the evolution of cementitious phases of sewer concrete after biogenic acid attack. Two concrete mixes; a blend of Sulphate Resisting Portland Cement and Fly Ash (SRPC+FA) and Calcium Sulpho-Aluminate (CSA) cement, with calcite and siliceous aggregates,...

Specifications for durability that are based on performance tests on concrete during the early stages of construction are finding acceptance throughout the world. In South Africa the durability index (DI) approach has been accepted into local specifications. This raises a challenge in the design of a concrete mixture for a construction project that...

We describe literature-based research on the viability of whole-culm bamboo as a construction technology for South Africa. South Africa has one bamboo species considered suitable for construction, namely Bambusa balcooa, found in various parts of the country. Quantitative production figures are not currently available; however, local reports indica...

The splash and spray and tidal zones are generally assumed to be the most severe marine exposure environments with respect to steel reinforcement corrosion in concrete structures. However, it has been observed in several aged marine structures along the Southern African coastlines, that there is usually relatively insignificant reinforcement corros...

Citation: Moore, A.; Beushausen, H.; Otieno, M.; Ndawula, J.; Alexander, M. Oxygen Availability and Corrosion Propagation in RC Structures in the Marine Environment-Inferences from Field and Laboratory Studies. Corros. Mater. Degrad. 2022, 3, 363-375. https://doi.org/10.3390/ cmd3030022 Academic Editors: Miguel-Ángel Climent and Carmen Andrade

This study investigated the properties of fine recycled aggregates (FRA), with a view to enhancing their properties for structural concrete applications. The study explored several approaches including mixing; curing; systematic screening of FRA particles below 1.18 mm to reduce the adhered cement paste (ACP) content; and the use of fly ash as 30%...

We report on the development of neutron-based techniques to non-destructively measure the composition of concrete. Previous experimental studies demonstrated the viability of the unfolding technique to determine the ratio of water, sand and cement in well-characterised concrete samples from the transmitted neutron energy spectrum. In this work, we...

The Durability Index (DI) approach used in South Africa is linked to transport-related properties of the cover layer of concrete. This performance-based approach utilises three different durability-related parameters, namely Water Sorptivity Index (WSI), Oxygen Permeability Index (OPI) and Chloride Conductivity Index (CCI). In the water sorptivity...

There is a growing trend to include service life (SL) and durability considerations in the design of reinforced concrete structures. This is partially a consequence of increasing deterioration of ageing concrete infrastructure worldwide and associated financial burdens and structural failures. Against this trend, this contribution critically explor...

The durability of a reinforced concrete structure or structural element relates to its capacity to withstand its exposure environment, without the need for major repair over its service life. Realising concrete durability may be achieved using service life design. Service life design methods are used to ensure sufficient resistance of concrete stru...

Progress in the establishment of a fast neutron beam reference facility for the non-destructive testing of concrete and other materials used in the nuclear industry is described. An additional area of interest is the development of methods for the independent verification of the alignment to regulatory codes of the constituent materials used in con...

The Water Sorptivity Index (WSI) test is one among three Durability Index tests in use in South Africa. It measures the rate of movement of a wetting front through concrete under capillary suction. Over the years, concern has been expressed as to the efficiency of saturation of the concrete specimens while conducting this test. The question relates...

SYNOPSIS The Water Sorptivity Index (WSI) test is one among three Durability Index tests in use in South Africa. It measures the rate of movement of a wetting front through concrete under capillary suction. Over the years, concern has been expressed as to the efficiency of saturation of the concrete specimens while conducting this test. The questio...

Numerous research efforts on metakaolin as a supplementary cementitious material (SCM) have been undertaken in the past 20 years. This material, while relatively expensive mainly due to low production volumes worldwide, nevertheless has a significantly lower production cost than Portland cement. However, industry remains tentative in considering me...

Ever increasing attention is being paid to deterioration prediction and service life modelling of reinforced concrete structures. Research has progressed to a stage where service life models and design philosophies are, to varying degrees, included in some codes and standards, such as the fib Model Codes and ISO 13823. This has helped to base pract...

This paper presents a comparative study on the corrosion rate and microstructural characteristics of Portland cement (PC) and calcium aluminate cement (CAC) -based concrete mixtures subjected to microbially-induced sulphuric acid (biogenic H2SO4) attack for 120 months in an outfall sewer. The higher amount of the amorphous AHx within the CAC-based...

The traditional prescriptive approach for concrete durability links mix design parameters such as w/b ratio, compressive strength and binder content to the expected concrete performance in aggressive environments. It fails to adequately take into account important factors such as binder type, chemical and mineral admixtures, and construction proced...

To investigate the influence of concrete quality and drying duration on steel corrosion rate when cyclic wetting and drying is used to accelerate corrosion propagation. To inform future similar experimental work in the area of accelerated steel corrosion in concrete. Concrete prisms (100 × 100 × 240 mm) were made using two w/b ratios (0.40 and 0.65...

The paper presents an overview of current knowledge and progress in service life design and modelling of concrete structures, taking an international view but also giving local examples from South Africa. It raises the question of why service life modelling is needed, and indicates that modern demands for longevity, durability, and sustainability o...

A global demand for affordable, sustainable, and durable concrete has resulted in growing use of Supplementary Cementitious Materials (SCMs). In the Western Cape Province of South Africa, the readily available SCM is Granulated Ground Corex Slag (GGCS), although fly ash can also be obtained. However, the availability of these SCMs, particularly GGC...

Structural design and application have always been linked to the compressive strength of concrete as the main relevant criterion. This was justifiable in the past, where concrete consisted of water, ordinary Portland cement and aggregates, but this concept is no longer relevant for modern and more sustainable cement and concrete. Despite these new...

This book provides an up-to-date survey of durability issues, with a particular focus on specification and design, and how to achieve durability in actual concrete construction. It is aimed at the practising engineer, but is also a valuable resource for graduate-level programs in universities. Along with background to current philosophies it gather...

The South African Durability Index approach is a performance-based method for specifying and assessing durability properties of reinforced concrete structures. This approach includes a laboratory-based oxygen permeability test, the results of which have been related to the prediction of carbonation rates in in situ concrete structures. The Swiss ap...

Durability index (DI) performance-based specifications have been implemented in the South African construction industry, mainly for large scale infrastructure projects undertaken by the national roads authority. DI test results have been compiled at the University of Cape Town (UCT) over the years 2008 – 2015. A large amount of this data is therefo...

The pore solution compositions of paste samples produced with Ordinary Portland Cement (PC), slag 25%, 50% and 75%, fly ash 30%, condensed silica fume (SF) 7%, and a ternary blend of 50% PC, 43% slag and 7% SF were determined. Not only are there significant variations in the concentration of the major cations and anions but also, and equally import...

In general, design approaches for durability can be divided into prescriptive design concepts and performance-based design concepts.

Concrete degradation due to microbially-induced acid attack in sewer systems is a frequently observed issue worldwide. Remediation and repair of sewer systems subjected to microbially-induced concrete corrosion (MICC) is complex and of high economic relevance. Numerous field campaigns and in-situ experiments are continuously being conducted in such...

This study investigated the effect of different drying regimes in the preconditioning stage on Durability Index (DI) test results. The moisture condition of specimens needs to be stable and uniform for the tests to be accurate and reliable. Three drying regimes were used: (a) standard oven drying method of 50°C for 7 days, (b) oven drying at 50°C t...

This paper reports on the microscopy quantitative imaging of some concrete pipe samples taken from an active experimental sewer section, and how the observed microstructure characteristics can be applied in the design of concrete mixtures used to manufacture sewer pipes. These samples have been subjected to microbially-induced sulphuric acid (H 2 S...

This chapter presents an overview on several performance-based approaches for concrete durability specification and conformity assessment of the as-built structure.

The chloride conductivity index (CCI) is a quality control parameter used to assess the resistance of concrete to chloride ingress. It is determined from the chloride conductivity (CC) test which has been in use in South Africa for close to two decades. During this time, it has undergone a number of changes to improve on its robustness, reproducibi...

Chloride-induced corrosion rate (icorr) prediction models for RC structures in the marine tidal zone that incorporate the influence of crack width (wcr), cover (c) and concrete quality are proposed. Parallel corrosion experiments were carried out for 2 1/4 years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated lab...

Parallel corrosion experiments were carried out for 2 1/4 years by exposing one half of 210 beam specimens (120 × 130 × 375 mm long) to accelerated laboratory corrosion (cyclic wetting and drying) while the other half underwent natural corrosion in a marine tidal zone. Experimental variables were crack width wcr (0, incipient crack, 0.4, 0.7 mm), c...

This study presents a novel framework for the design of reinforced concrete (RC) structures which aims at ensuring that future RC structures have the lowest possible carbon footprint, energy use and impact on the environment. The key focus of the study is on RC structures where there is often a lack of grasp of materials aspects, and environmental...

To present resistivity-based chloride-induced corrosion rate prediction models and hypothetical framework for interpretation of resistivity measurements in cracked RC structures. Parallel corrosion experiments were carried out by exposing one half of 210 beam specimens (120 × 130 × 375 mm) to accelerated laboratory corrosion (cyclic 3 days wetting...

The corrosion of steel reinforcement due to carbonation of concrete presents one of the major deterioration mechanisms in reinforced concrete structures. The South African concrete durability design method for reinforced concrete structures incorporates a performance based approach to evaluate the penetrability and quality of the concrete cover. Wi...

The paper reviews the current status of service life prediction and performance testing for concrete structures. Part I emphasizes the advantages of performance-based approaches to durability prediction, from which flows service life modeling. It also deals, inter alia, with issues around performance specifications, durability indicators, and devel...

Durability problems in reinforced concrete (RC) structures are an issue of global concern, since they threaten economic growth, natural resources and human safety. As a result, attempts have been made in design standards developed in most countries to include requirements to provide durable RC structures. This paper examines and compares such durab...

Durability problems in reinforced concrete (RC) structures are an issue of global concern, since they threaten economic growth, natural resources and human safety. As a result, attempts have been made in design standards developed in most countries to include requirements to provide durable RC structures. This paper examines and compares such durab...

Innovative research in the use of concrete has made it one of the most commonly used materials in the construction industry globally, with about 25 billion tons consumed annually. The durability of concrete is strongly dependent on the interactions of its constituent materials with the environment, and determines its performance during the service...

Laboratory simulation of the process of formation of sulphuric acid (H2SO4) on the non-submerged walls of concrete sewer pipes, and subsequent attack of products of cement hydration, has proved to be a challenging task over the years. This, coupled with scarce facilities for in-situ measurements, has generally contributed to the lack of a more comp...

The paper reviews the performance of cementitious materials under conditions of biogenic corrosion of concrete sewer pipes. It draws on data from samples analysed in the laboratory and also installed in an experimental sewer in South Africa, as well as data from sewers in France and work from simulation chambers in Germany. Cementitious materials,...

The effect of different quantities of admixed superabsorbent polymers (SAP) on durability and strength properties of normal strength mortars containing various binary cement blends was investigated. Addition of SAP did not significantly affect compressive strength, although a slight retardation of strength development was observed in mortars with h...

The production of clinker, the main constituent in cement, is highly energy intensive. Its production results in considerable CO2 emissions from raw materials and fuels burnt during manufacture. The current environmental concerns and policies developed to address this have resulted in increasing pressure on cement producers to reduce CO2 emissions...

The extensive deterioration of reinforced concrete (RC) structures in the recent past has raised worldwide concerns. To ensure efficient utilization of resources (sustainable construction) there is a need to construct durable RC structures. The current quality control approach of measuring strength of standard specimens such as cylinders or cubes i...

The paper deals with issues of durability in reinforced concrete. It briefly describes the shift from prescriptive specifications to performance-based specifications with an overview of the South African approach to durability design and specifications. An example is provided that illustrates the first large-scale implementation of the approach in...

Acid testing of concrete specimens is not simple. Questions to be considered are: the type of acid to be used; the representativeness of the concrete mixtures tested; the nature of the measurements to characterise degradation; and how the results are to be applied to practical design and prediction of service life. It was mentioned in

This paper describes a study on the durability potential and strength of composite Portland-limestone cement (PLC) concrete mixtures blended with ground granulated blast furnace slag (GGBS) and/or fly ash (FA). Their performance was compared against ordinary Portland cement, plain PLC and Portland-slag cement concrete mixtures. Using the South Afri...

Three ground granulated slags (FeMn arc-furnace (GGAS), Corex (GGCS) and blastfurnace (GGBS) slags) of varying chemical composition, and from different sources were used to make concretes using two w/b ratios (0.40 and 0.60) and three slag replacement levels (20, 35 and 50%). The effect of chemical composition and replacement level of slags on the...

Concrete and cement-based materials must operate in increasingly aggressive aqueous environments, which may be either natural or Industrial. These materials may suffer degradation in which ion addition and/or ion exchange reactions occur, leading to a breakdown of the matrix microstructure and consequent weakening. Sometimes this degradation can be...

In the recent past there have been rising concerns on the lack of durability of reinforced concrete (RC) structures. A measure of strength for quality control has been identified as inadequate in the control of structures quality with regard to durability. Proposals have been made for a shift to performance-based specifications. This paper discusse...

This paper advocates for the adoption of performance-based limiting crack widths with respect to steel corrosion in reinforced concrete structures. The authors argue that, from both durability and sustainability viewpoints, the practice of adopting a universal limiting crack width for a wide range of in-service exposure conditions and concrete cove...

The objective of the paper is to provide an understanding of the South African concrete industry's environmental burden in terms of natural resource consumption and carbon dioxide equivalent emissions (CO2-e). The review covers current practices in the concrete construction field in South Africa (SA) and their implications for the environment. Elab...

Natural steel corrosion of reinforced concrete (RC) structures is a slow process which researchers find necessary to accelerate in laboratory tests to obtain needed damage in a short time. Regrettably, there is no standard procedure for accelerating steel corrosion in RC specimens. Researchers therefore continue to use various techniques to acceler...

To show the application of the chloride conductivity index test in service life prediction (SLP) using both the deemed-to-satisfy and probabilistic approaches to performance-based durability design. It is desirable to adopt a performance-based approach with respect to durability design of reinforced concrete (RC) structures. This is based on the pe...

This research investigated fresh and hardened properties of concretes containing three different types of slag at three different replacement ratios and three different water/binder ratios. The three types of slag include ground granulated blastfurnace slag, ground granulated Corex slag and a ground granulated ferro-manganese arc furnace slag. Diff...

Structural engineers rely on measurable parameters of corroding RC structures to predict their residual load-bearing capacities. The most widely used parameter is cracking of the cover concrete. This paper looks into the potential of using longitudinal strains and stiffness of corroding RC beams to predict the level of steel corrosion in the beams....

The paper describes a study that examined and compared the potential durability performance of various geographically distinct South African marine concrete mix types. Mix proportions were designed at two water/binder ratios (0.40 and 0.55) for different material combinations of binder and aggregate types. Sampling was done at 28, 91 and 182 days....

The durability of reinforced concrete (RC) structures is dependent on the resistance of the concrete cover to ingress of aggressive substan- ces from the environment that initiate and sustain the corrosion process. The concrete cover’s resistance is dependent on its thickness and penetrability. In South Africa, the performance-based approach develo...