A direct method which was useful for repeated quick tests was presented to determine the bond anchorage length for 3/8 inch diameter strand and the distribution of bond forces within the anchorage length. Seventy-four specimens were tested. Three different cross sections were tried, namely 4 in. x 4 in., 3 in. x 3 in. and 2 in. x 2 in. Two types of load conditions were tested, tensioned and untensioned. From the experimental results it was observed that friction appears to be the major component determining the bond strength. The bond strength of strand does not appear to be significantly affected by the degree of initial steel stress in concrete. The anchorage length for 3/8 inch diameter rusted strand was found to be between 8 and 10 inches for a force of 13 to 14 kips. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

Studies in Reinforced Concrete involving transference of stresses by bond from steel to concrete require a method for strain measurement in concrete reinforcement which is reliable and free from local effects. A very simple and economical method based on a technique first used by Brice⁶, has been developed using ordinary etched foil electrical resistance strain gauges, applied to the interior of a split pipe, which is joined together by a room-temperature epoxy adhesive, before embedment in concrete as reinforcement. Experiments performed to prove the reliability of the Technique have given indications that stress transference by bond is affected by the volume of concrete surrounding the reinforcement. Some supporting evidence from the results obtained by previous investigators⁴'¹² is presented. Also observed during the "proving experiments" is the pronounced effect of cracks on strain measurements, and the regular spacing of cracks in tensile specimens. A cast-in-situ joint between precast and prestressed members has been studied with the help of the modified technique, and the results point to the formation of micro-cracks detected by local variations in strain measurements which precede visible cracking. These variations, however, tend to disappear on higher or cyclic loading. Also observed during the joint test is the composite action even after complete horizontal slip between the cast-in-situ and precast concrete, provided the two portions are prevented from further slipping, and at high loads when slip is allowed to occur, it is seen that a moment mechanism other than in the composite section governs vertical forces in the stirrups. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

This paper describes how the author studied the "workability" of freshly mixed concrete. Workability is a very important and necessary property which forms part of the specifications for concrete but its meaning is rather vague. Concrete is usually required to have a certain slump or flow, as determined in a standard manner, with standard apparatus, but the readings obtained are comparative only and have no absolute value. The question which the author asks and tries to answer is, can we treat freshly mixed concrete as a fluid and measure its absolute viscosity and if so how are slump and flow etc. related to it? What does slump and flow really mean in terms of absolute units? An apparatus was developed which does measure a quantity similar to viscosity and values were obtained for nine different mixes. Readings were however obtained at only one velocity so that the non-Newtonian behaviour of the concrete was not investigated. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

The design of tilt up concrete wall panels was studied in this paper. Design charts were developed to assist the engineer in the analysis of panels under load. Computer simulation of the concrete section was used to obtain the chart data. A computer study of the effect of a number of parameters on the load carrying capacity of wall panels was made. Loading, section properties and support conditions were varied in isolation in an attempt to obtain general trends of how each influences the strength characteristic of a concrete wall panel. A recommended design procedure has been included which utilizes the charts developed. / Applied Science, Faculty of / Civil Engineering, Department of / Graduate

No description available.

No description available.

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.