There is a dearth of clear and consistent information on the effects of mix design parameters, and their corresponding interactions, on restrained shrinkage cracking in non-structural concrete patch repair mortars (PRMs). This dearth of information makes the design and development of PRMs with improved resistance to cracking challenging. The problem is further compounded by the fact that the existing code of practice for concrete repair - the EN 1504-3:2005 - specifies many material properties such as chloride ion content, compressive strength, bond strength, skid resistance and capillary absorption. Some of these material properties, such as skid resistance and chloride ion content, are not relevant to cracking. Also, empirical analytical models for predicting stresses and the age at cracking in PRMs need improvement to accommodate recent developments in materials such as admixtures and additives. Accurate prediction models help design engineers make informed choices during the selection of PRMs. The principal objective of this study was to generate new knowledge that would inform the design of non-structural PRMs and the development of performance requirements for these PRMs. This was accomplished through an investigation into the influence of multiple mix design parameters and crack-determining material properties on restrained shrinkage cracking, involving a critical review of literature and a comprehensive laboratory experimental programme. The experimental work was organised into two phases. Phase one entailed an investigation into the effect of water content, binder content, binder type, curing type, shrinkage reducing admixture (SRA) dosage, polymer type and polymer content on cracking. A 2⁵ full factorial experiment approach with three replicates was used in this phase. 32 mixes were studied. The sensitivity of cracking to the listed mix design parameters was determined with respect to the age at cracking in ring specimens made in accordance with ASTM C 1581. A trend analysis of the investigated mix design parameters and cracking was also done.

The acceptable performance levels and serviceability of reinforced concrete (RC) structures are always the priorities of asset managers, engineers and researchers in any country. RC structures in service may fail to adequately perform due to changes in functionality, corrosion attack on the reinforcing bars, lack of proper and timely maintenance, and loading and standards updating, among other reasons. Impact loading is an extreme form of loading that can damage RC structures such as bridges, interchanges and flyovers during their life span. The repair and strengthening of deteriorating RC structures in service, by using concrete patch repairs and fibre reinforced polymers (FRP) respectively, has attracted a lot of attention from researchers and engineers. Nevertheless, these rehabilitated RC structures in service are susceptible to future deterioration with adverse effects. Inspection and periodic maintenance of strategic RC structures in use are essential for their safe serviceability and to avoid or mitigate economic loss. This experimental study was conducted on fifteen RC beams with the size of 155 x 254 x 2000 mm, in order to study their behaviour under impact loading testing. Twelve out of these fifteen RC beams were intentionally damaged by uniformly reducing 14 % of the cross-section of their main reinforcing bars, as this simulated the effects of corrosion on RC structures. The drop test, with the impactor applied from varying drop heights, was selected from the different types of impact loading testing methods and used in this research. Each tested RC beam was subjected to eight consecutive drop tests. During this experimental study 120 tests were performed and, from these tests, dynamic responses were recorded for analysis. Two transducers, a load cell and high-speed camera (HSC), were used to record data. In general the captured and stored dynamic responses led to the extraction of contact forces and deflections results. In addition, the HSC recorded video footage of the impact scenarios of the RC beams. The combined use of software such as Photron FASTCAM Analysis (PFA) and Matlab R2014a enables the acquisition of deflection results and, on the basis of these results, residual deflection

The repair and maintenance of ageing reinforced concrete (RC) structures has become increasingly costly, especially in the Cape Peninsula. Protection and maintenance of these reinforced concrete structures against concrete deterioration and rebar corrosion have become far more important for road authorities and asset managers. City Engineers are responsible for the repair and rehabilitation of RC structures in different exposure conditions, by identifying the type of deterioration and then employing the correct concrete repair solutions or corrosion resistance measures. This dissertation investigates the environmental exposure conditions in the Cape Peninsula that result in chloride-induced and carbonation-induced corrosion of reinforced concrete structures in the region. It includes a literature review on concrete deterioration mechanisms and the role of aggressive elements in rebar corrosion. The literature review also considered alternative corrosion-resistant rebar. There are a number of available alternatives, which include Fiber Reinforced Polymer (FRP), Hot Dip Galvanized (HDG) steel, and Stainless Steel rebar. Each alternative has advantages and disadvantages depending on design applications and durability requirements. The use of corrosion-resistant rebar would increase the structure's longevity, thus providing long-term cost saving for road authorities. In the City of Cape Town, city engineers have standardised the use of HDG rebar for repair solutions and new concrete structures. HDG improves corrosion resistance, thus making it desirable to road authorities. The HDG process has been developed in the construction industry with low production time and cost, proving favourable factors for engineers. In addition, engineers have to improve concrete quality and construction methods to protect the underlying rebar from corrosion. On a technical level, HDG rebar use in RC structures has benefits which outweigh their cost implications. The exclusive use of HDG rebar without sound engineering judgment based on factors such as the location of the structure, distance from the coast, the structural loading conditions, and construction methods and quality standards, might not ensure better concrete durability and structural longevity. Generally, correct structural rebar design and concrete quality can eliminate the need for the use of corrosion protection methods and materials. The use of HDG is a very attractive solution for structures within 5km from the coast; otherwise, normal steel is suited for most applications. Reinforced concrete members such as concrete bollards, bridge handrails and balustrades can be treated as consumables and can be replaced once steel corrosion or concrete deterioration has occurred and becomes unsightly, which would be about 20 years. This approach would be economically advantageous and politically favourable to the road authority as it creates skills and jobs by reducing initial internal and contractual costs. To illustrate the common forms of rebar deterioration in the Cape Peninsula region, this dissertation has included five repair and rehabilitation projects completed by the City of Cape Town's Road Authority. These rehabilitation projects have been identified for concrete repair and rehabilitation works, and some of these structures have recently undergone extensive concrete rehabilitation. City engineers are faced with many challenges that hinder service delivery, engineering processes and effectiveness. Among these are lack of staff with experience in concrete repair and asset management, and the lack of proactive maintenance tools. The lack of an adequate Bridge Management System (BMS) contributes to the inefficient allocation of resources for rehabilitation and repair projects. The Supply Chain Management System also delays the appointment of appropriate contractors due to unwieldy management systems and bureaucracy. These systemic problems are discussed to provide a better understanding of the current selection of concrete repair systems.

In practice, concrete is initially tested for compressive strength by casting a cube/cylinder, which is left to cure in favourable conditions until the date of testing. The results obtained from such tests can give a consultant guidance on the material's properties such as estimated porosity, density and compressive strength. These tests are known as control and conformity tests. Supplementary tests may be needed if the control test fails or further investigation must be done to the concrete. These tests are done by drilling core specimens out of the in-situ concrete and applying the necessary tests. These results are used to verify conformity with specifications set out by the engineer. The outcome of such a test is extremely important as it is often used as the basis to decide the integrity of the structure. Although important, in-situ compressive strength remains as one of the least understood concrete properties due to the difficulty in relating and interpreting the results. Furthermore, there is no reliable universal relationship between compressive strength of cores and; moulded cubes and cylinders. A comprehensive literature and experimental study was attempted to relate standard cube and core compressive strength, as well as, cylinder and core strengths to identify the factors that may affect the analysis and interpretation of results. An experimental program was set out to relate the compressive strength of cubes, cores and cylinders, with a length/diameter ratio of 1.0. All specimens were cast, cured, prepared and tested in the University of Cape Town, New Engineering Building (NEB) laboratory according to South African National Standards. Twelve concrete mixes were designed using two concrete strengths (30 and 50 MPa), three maximum aggregate sizes (9.2, 19.2 and 26.5 mm) and two aggregate types, namely greywacke and quartzitic sandstone. An additional two mixes of high strength concrete were created (60 and 75 MPa) using 19.2mm greywacke aggregate. The compressive tests involved a 100 mm cube, three diameter cylinders (70, 100 and 150 mm) and four core diameter sizes (50, 70, 100 and 150 mm). All core specimens were drilled from beams that were cast. A total of 520 specimens were tested during this study. An analysis of variance (ANOVA) was applied to all the results to identify if the compressive strengths were statistically significantly different. The compressive strength and statistical results indicate that 100 mm cubes and 100 mm diameter cores have statistically similar compressive strengths. The diameter of the core and cylinder influenced the compressive strength. It was found, as the diameter size decreased the strength increased for core specimens and the opposite was found for the cylinder. Both findings were inconsistent with literature. However, as the core and cylinder diameters increased to a size larger than 100 mm, the compressive strengths were statistically similar. With respect to the maximum aggregate size, the strength was influenced in correspondence with the diameter size. As the core diameter decreased and the maximum aggregate size increased, the compressive strength increased. Whereas, the opposite was found with the cylinders. The strength level further determined the influence that the coarse aggregate type had on the compressive strength. At the 30 MPa strength level, the aggregate types produced statistically similar strength. At the 50 MPa strength level, the sandstone produced a statistically higher compressive strength compared to the greywacke aggregate. Finally, as the strength level increased over 50 MPa there was no significant difference between the mean compressive strength of cubes and cores. It was concluded, owing to the controlled environment that the all specimens were cast, cured, prepared and tested; as well as the similarity in the geometric size, statistically comparable compressive strengths were obtained for cubes and cores.

Call number: LD2668 .T4 1951 S65 / Master of Science

Durability is a major concern for reinforced concrete (RC) structures. RC structures both in service and new, are subject to cracking. Irrespective of the cause of the cracking, cracks can increase the rate of penetration of aggressive species into concrete and modify the transport properties. Consequently, the service life of corrosionaffected RC structures may be drastically reduced in the presence of cracks. However, no modifications are made for the influence of cracking on the penetration of aggressive species into concrete when analysing durability test results or making service life predictions, even through concrete is very often in a cracked state. This study focused on the influence of cracks on the ingress of aggressive species (carbon dioxide and chlorides) into cracked concrete in comparison to uncracked concrete. The aim was to establish any correlations between the transport properties in uncracked and cracked concrete. Furthermore, in a broader context, the aim was to assess to what extent the modified cracked concrete parameters used in service life predictions affect the service life outputs, when compared with service life outputs obtained using the uncracked concrete parameters. Six concretes mixes were investigated comprising two water/binder (w/b) ratios (0.40 and 0.55) and three binder types (100% CEM I 52.5N (PC), 70/30 PC/FA and 50/50 PC/GGBS). 100 x 100 x 500 mm beams were cast and cracks were induced after seven days in the mid-span of each beam using three-point loading. Two crack width ranges were investigated; 0.1-0.4 mm (wcr1) and 0.5-0.8 mm (wcr2). The central section of the beam that contained the crack was sawn from the rest of the beam and used for either accelerated carbonation or bulk chloride diffusion testing. Cores were drilled from the outer sections of the beam and used as specimens for the Durability Index tests. The cracked specimens were monitored for carbonation (accelerated carbonation) and chloride ingress (bulk diffusion), while the uncracked ones were monitored for durability parameters (OPI, WSI & CCI) after 8 and 16 weeks of exposure. Firstly, it can be concluded that the presence of cracks modifies the transport properties of concrete by promoting rapid increase of ingress of aggressive species (CO₂ & Cl-) into the concrete matrix. It was found that the degree to which the transport properties were modified increased as the crack width increased. This was primarily attributed to the increase in surface area created by the crack, which allowed increased amounts of species (CO₂ & Cl-) to penetrate into the concrete matrix. In the case of carbon dioxide ingress, the presence of cracks significantly increased the rate of carbonation (up to 50 %) in the concrete specimens that contained blended cements PC/FA and PC/GGBS when compared to the PC concrete specimens. However, in the case of chloride ingress the effects of cracks in the PC mix resulted in the highest presence of chlorides (up to 78 %) in the concrete specimens in comparison to the chlorides present in the PC/FA and PC/GGBS concrete specimens. Secondly, when the sound (DI) and cracked durability parameters (carbonation and diffusion coefficient) where used in carbonation and chloride ingress service predictions, it was found that the DI service life prediction outputs were more conservative in relation to service life outputs from the durability parameters obtained from cracked concrete specimens. These results highlighted the degree of influence which the presence of cracks had on modifying transport properties in concrete. Furthermore, it also highlights the impact of the presence of cracks on the service life of RC structures and the prediction of long-term carbonation- and chloride- induced corrosion. Due to the significant influence that cracks have on modifying the transport properties of concrete, the results show that some reduction factors need to be applied to the results from the DI approach to reflect a more realistic durability potential of the concrete. Further research into understanding how other crack parameters (crack depth, frequency etc.) modify transport properties in concrete will lead to a more accurate insight into dealing with and accounting for the presence of cracks in RC structures.

Wastewater conveyance and treatment facilities, which include outfall sewers, manholes, and treatment works, are among the key constituents of a country's infrastructure. Most of these facilities are made of concrete due to its low production costs, versatility, inherent strength and durability under most conditions. However, under certain conditions, sewage that is conveyed through outfall sewers becomes septic and hydrogen sulphide (H2S) gas is generated. When this gas is released from the sewage and absorbed onto the moist concrete sewer pipe walls, it is microbially converted by sulphide-oxidising bacteria to sulphuric acid (biogenic H2SO4) which reacts with the acid-soluble components of concrete causing it to corrode. In principle, the biogenic H2SO4 concrete corrosion mechanism entails simultaneous destruction of the calcium hydroxide (CH) in the hydrated cement paste (HCP) and substituting a larger molecule of calcium sulphate into the concrete matrix thus causing pressure and spalling of the adjacent concrete and aggregate particles. In addition, the calcium sulphate precipitates as gypsum which reacts with various aluminates to form secondary ettringite. These mechanisms lead to the loss of stiffness and strength, accompanied by expansion and cracking, and eventually transformation of the affected concrete matrix into a soft and pulpy non-cohesive layer. The biogenic concrete corrosion rate depends, inter alia, on the chemical composition of binders (cement and supplementary cementitious materials (SCMs)) and microstructural characteristics of concrete mixtures used in the manufacture of sewer pipes. The needed properties of concrete mixtures for sewer pipe applications can be determined by biogenic corrosion prediction models, such as the widely used deterministic (mechanistic) Life Factor Method (LFM). The service life of wastewater treatment facilities made of concrete depends on the input parameters in corrosion prediction models. The motivation behind the current study was based on the need to improve the ability to predict the design life of concrete sewers by improving the input parameters in the LFM, which is used in South Africa. The design life of concrete sewers in South Africa has traditionally been 40 years. The main objective of the current study was to characterise the microstructure of both Portland cement (PC) and calcium aluminate cement (CAC) based concrete mixtures that had been subjected to biogenic corrosion mechanisms in an operational sewer environment for approximately 127 months (10½ years); further, based on the understanding of the underlying mechanisms of attack, proposals were made to improve the LFM, for which the corrosion rate-controlling input parameter, referred to as alkalinity (or equivalent CaCO3, as a summation for both binder and aggregate) is based on the characteristics of plain PC-based binder systems. In addition to the main objective above, a parallel study was undertaken to characterise parameters that influence biogenic concrete corrosion rates based on measurements taken in two sewer environments/sites in different geographical locations in South Africa. One of the study sites was the Virginia Experimental Sewer (VES) in Virginia, Free State Province, while the other site was a manhole within the Langa Pump Station in Cape Town, Western Cape Province. The VES consists of 900 mm diameter by 300 mm long concrete pipe samples made from both PC- and CAC-based (plain and blended) binder systems, the top 120° being cut to form 'lids', so that they are removable. The removable 'lids' enable scheduled observations and sample recovery to be undertaken. Moreover, the 'lids' also act as windows through which core samples can be placed in plastic baskets that are hung at certain sections in the sewer headspace, so that they can be accessed for monitoring.

M. Tech. Civil Engineering / The re-use of waste materials is promoted for the preservation of non-renewable natural resources. Glass waste was investigated as partial cement and aggregate replacement in concrete. Two types of soda-lime waste glass: Superfine Glass Waste and Ceramic Stone and Porcelain glass waste, residues of glass recycling processes, were used for the experimental programme. This study focused on the reuse of glass waste in concrete in optimal mix proportions, to partially replace cement and aggregates; for low cost housing, concrete applications and greening of the environment.

Twenty five model beams were progressively loaded to failure in order to investigate the influence of the following variables on the behaviour of reinforced concrete deep beams : i) Concrete compressive strength ii) Reinforcement iii) Geometry. The model beams were all of 1500mm span, with a depth of 750mm. This span to depth ratio of 2 corresponds to the upper limit, to which the recommendations for deep beam design applies, as provided by many current codes of practice. Methods currently in use for the design of reinforced concrete deep beams were reviewed and compared. The experimental results were compared with the predictions of these design methods. This comparison revealed a large lack of agreement in the predictions of the cracking and ultimate strengths of deep beams.

Extensive research to determine the strength of steel deck reinforced concrete floor systems has been carried out on single-span, single panel width test specimens. Little of this research has considered the benefits that actual field conditions have on overall strength and stiffness. This experimental study investigates typical field details at intermediate supports and end spans. In particular, the influence of adjacent spans and typical pour stop details are considered. Additionally, this study illustrates the applicability of simple analytical models, which can be used to determine the strength and stiffness of steel deck reinforced concrete floor systems. / Master of Science