Browsing by Author "Alexander, Mark G"

Now showing 1 - 3 of 3
  • Thumbnail Image
    Item
    Restricted
    The acceptability of concrete block construction in low cost housing in the Cape Peninsula area
    (UFS Department of Quantity Surveying and Construction Management, 2002) Bredeveldt, Toni K; Alexander, Mark G; Bowen, Paul A
    This article presents the findings of a research project examining the acceptability of concrete block construction for low cost housing in the Cape Peninsula in terms of materials and execution. Data were collected by means of a questionnaire survey in which residents of low cost housing were interviewed. In addition, personal and telephonic interviews were conducted with key stakeholders from the construction industry involved in the delivery of low cost housing. The findings indicate that concrete block construction is being used extensively for low cost housing developments in the Cape Peninsula, owing to its defining characteristics such as ease of construction, affordability, durability, speedy delivery and acceptance. End-users are generally satisfied with the construction material used for the wall structure of their current houses. They are, however, dissatisfied with the workmanship of the construction, as they feel that problems such as cracking and damp have arisen because of hurried and incomplete construction. The end-users are aware that the wall structures are not plastered, but only bagged, Even without any formal or technical knowledge of building houses, they state that they should be involved in the planning and construction stages of their new homes with regard to funding and appearance in order to make these homes more affordable and acceptable. Despite a lack of technical knowledge of concrete technology, the respondents felt that the concrete block was the most acceptable form of construction material available for wall structures because of its perceived strength and durability.
  • Thumbnail Image
    Item
    Open Access
    The influence of curing techniques and chemical admixtures on the properties of concrete
    (2012) Martin, Michael; Beushausen, Hans-Dieter; Alexander, Mark G
    The deterioration of concrete in South Africa is becoming of major concern to the construction industry. The maintenance of reinforced concrete structures is an extremely expensive exercise and is a continuing necessity. Concrete curing is a practice that is understood to be a necessity within industry, but is often overlooked as a result of time and/or economic constraints. The objective of the study is to ascertain whether or not the implementation of better quality and alternative curing techniques will improve the durability properties of the concrete. Curing is defined as the maintenance of appropriate moisture and temperature conditions to permit the continuation of the hydration or pozzolanic reaction. The objective of curing is to ensure the progress of hydration reactions causing the filling and discontinuity of capillary voids by hydrated compounds in newly placed concrete. Modern curing methods are generally classified as wet or sealing. Wet methods include fogging, sprinkling, ponding, immersion and wet coverings. Sealing methods include plastic coverings and membrane forming curing compounds. Crystallising permeability reducing admixtures may be included in the concrete mix design in order to decrease the penetrability of concrete by decreasing the interconnectivity of the pore structure. Curing methods need to be employed in order to assure specified durability limits are acquired, as durability constraints are implemented in industry. Various methods of curing were tested in order to establish the effect of the techniques on the durability properties of concrete. Samples were placed in water and in winter (Western Cape, South Africa) and simulated summer environments. Various curing techniques were then employed within each of the exposure environments. The curing methods were damp hessian, cling wrap, two curing compounds and two crystallising permeability reducers (PRA's). Samples were also left untreated in each environment as reference samples. Compressive strength, oxygen permeability, water sorptivity, chloride conductivity, bulk diffusion and accelerated carbonation tests were conducted. The results obtained in the study concur with those presented in literature. Prolonged periods of moist curing are significantly beneficial to the compressive strength and durability properties of concrete , however, full water immersion is not a feasible alternative for large or insitu-cast concrete elements. Results of the study show that d amp hessian was the best method to ensure superior durability properties. The sealing of samples with curing compounds in a cool and wet environment (winter) is not recommended, whereas it is marginally beneficial, as was clingwrap, in a hot and dry environment (summer). The crystallising PRA's provided mixed results and were favourable where excess moisture was available and fairly ineffective in dry conditions. The durability properties of concrete are markedly affected by the curing technique implemented .
  • Thumbnail Image
    Item
    Open Access
    Investigating repair mortars containing superabsorbent polymers as a method of internal curing to improve concrete patch repair performance
    (2012) Gillmer, Marc; Beushausen, Hans-Dieter; Alexander, Mark G
    Concrete structures are designed with a specific service life in mind and deteriorate over time due to their exposure to environmental conditions. In order to increase the service life of concrete structures, they can sometimes be rehabilitated and repaired using concrete overlays. However, problems may develop between the new and old concrete due to differential shrinkage between the concrete substrate and overlay. These differential shrinkages typically result in the build - up of tensile stresses within the overlay. If the concrete does not possess sufficient tensile strength, the overlay will crack and or delaminate, which is usually considered failure. To prevent cracking, the quantity of shrinkage that occurs in the overlay needs to be minimised. Literature suggests that the addition of superabsorbent polymers (SAP's) to the concrete overlay can reduce the total shrinkage that occurs. A large amount of research exists pertaining to the use on SAP's in high performance concrete (HPC), while very little research has been done regarding their influence of overlays. This research investigated how the addition of SAP's to overlays containing silica fume (SF) would improve bonded concrete overlay performance. Testing was conducted on overlay samples with a water:binder (W/b) ratio of 0.45 and 0.55 with SAP contents of containing 0%, 0.2%, 0.4% and 0.6% of the total binder content. Samples were subjected to a large number of tests including compressive, tensile and shear bond strength, durability, tensile relaxation, elastic modulus, carbonation, bulk diffusion and free and restrained shrinkage. The results of this research indicate d that the SAP's had a greater influence on samples with a higher w/b ratio. The results also suggested that an increase in SAP content resulted in improved tensile strength, tensile relaxation and durability while also reducing the rate of drying shrinkage at early ages . This indicated that SAP's can be used in mix design to improve bonded concrete overlay performance.