Browsing by Author "Arito, Philemon"

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    Discrete sacrificial anodes and their use in service life extension of chloride contaminated reinforced concrete structures
    (2012) Arito, Philemon; Beushausen, Hans-Dieter; Alexander, Mark G.; Otieno, Mike
    There is an urgent need for economic and technically sound concrete repair technologies in South Africa as the number of deteriorating RC structures needing repair is increasing. Currently, the South African concrete repair industry mainly relies on the application of patch repairs and corrosion inhibitors while other potentially successful methods such as sacrificial anodes are rarely applied. Sacrificial anode cathodic protection (SACP) systems use metals that are higher than steel in the electrochemical series. These metals corrode preferentially to steel thereby supplying electrons to the cathodic steel surface. Common SACP systems include discrete zinc anodes installed in slots or drilled holes, non -structural jacket encasements, and overlays made from expanded zinc mesh or any other convenient form. The effectiveness of discrete SACP systems in service life extension of chloride contaminated RC slabs has been investigated in this study. Similarly, the extent to which discrete sacrificial anodes can be used to extend the service life of corroding chloride contaminated RC structures has been assessed through an extensive review of literature a s well as laboratory experiments on corroding chloride contaminated RC slabs . This study evaluates the performance of discrete SACP systems with respect to binder type, corrosion rate and the level of chloride contamination with an objective of developing guidelines for rational concrete repair when using SACP systems to repair RC structures that are deteriorating from corrosion of reinforcing steel in South Africa. Eight slabs were investigated. Four slabs were cast using 100% PC CEM 1, 42.5N while the other four were cast using a blend of 70/30 PC CEM 1, 42.5N/FA. Each slab comprised two portions: one half of each slab was cast using concrete that was admixed with 0.6% chloride by mass of binder while the other half was cast using concrete that was admixed with 1.8% chloride by mass of binder. The corrosion in the slabs was induced and accelerated using direct anodic current. The SACP system that was used in this study comprised discrete zinc disks put in a cylinder of a proprietary high alkaline mortar. The se anodes were installed in 1 0 0 x 10 0 x 60 mm deep cavities that had been made in concrete. The anodes were connected to the reinforcement cage using tie wires and thereafter backfilled with a repair mortar. The cavities in which the anodes were installed were arranged in a square grid of 450 x 450 mm. The corrosion rate and half-cell potential of the steel as well as the resistivity of concrete in the slabs were monitored over a duration of five month s. The discrete SACP system that has been investigated in this study can increase the service life of chloride contaminated RC structures that are deteriorating as a result of rebar corrosion. The discrete anodes reduced the corrosion rate of steel in the test slabs. The percentage reduction in the average corrosion rate was higher within the slabs that were cast using 100% PC CEM 1, 42.5N than in the slabs that were cast using a blend of 70/30 PC CEM 1, 42.5N/FA. The reduction in average corrosion rate within the slabs cast using 100% PC CEM 1, 42.5N ranged between 45-95%. Similarly, the reduction in the average corrosion rate of within the slabs that were cast using a blend of 70/30 PC CEM, 42.5N 1/ FA ranged between 54-75%. Throughout the test specimens, the portions of the slabs that was admixed with 0.6% chloride by mass of binder exhibited superior performance. These portions (admixed with 0.6% chloride by mass of binder) experienced the greatest reduction in average corrosion rate as well as the greatest shift in average half -cell potential towards values that are more negative. Finally, in order to achieve the long-term objective of increasing the service life of RC structures that are deteriorating as a result of rebar corrosion, lo ng-term studies ought to be undertaken to ascertain, with surety, the effectiveness of discrete SACP systems in corroding structures.
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    Influence of mix design parameters on restrained shrinkage cracking in non-structural concrete patch repair mortars
    (2018) Arito, Philemon; Beushausen, Hans-Dieter; Alexander, Mark Gavin
    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.
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    Investigating the performance requirements for proprietary concrete repair materials with respect to durability and cracking resistance
    (2021) Vukindu, Brian; Beushausen, Hans-Dieter; Arito, Philemon
    The premature deterioration of recently constructed concrete structures leads to the need for remedial measures to reinstate their safety and/or serviceability. Bonded concrete overlays (BCOs) are the most widely used concrete repair technique. The premature failure of these overlays, often manifested by cracking and/or debonding, is common despite their widespread use. There are many repair standards, codes and technical guidelines for BCOs. The performance requirements for BCOs stated in these standards vary. This makes the specification of repair materials difficult. This problem is further compounded by the existence of many proprietary concrete repair materials. The objective of this study was to investigate the performance requirements for proprietary repair mortars on cracking resistance and durability with respect to EN 1504-3:2005. This was achieved through an investigation of the mechanical, durability and transport properties of proprietary repair mortars in the hardened state. The mechanical properties that were tested comprised: compressive strength, tensile strength, elastic modulus, tensile relaxation, restrained shrinkage cracking and drying shrinkage. Durability index tests of OPI, CCI WSI were also done. Twelve proprietary repair mortars were tested in the laboratory. Their chemical and physical characteristics based on the aforementioned material properties were determined. The mortars under investigation exhibited significant differences in their physical properties and chemical composition. A review of the existing performance criteria, as stipulated in EN 1504-3:2005, was also conducted to determine if the repair mortars under investigation conform to the requirements of this code. From the test results it has been noted that the tested proprietary repair materials achieved the compressive strengths as stated by the standard EN 1503-4:2005. 11 of the tested repair materials were categorised as “structural” with only mix P2 being a “non-structural” repair mortar. These results also confirmed the specifications/categorisation from the manufacturers. Mixes PS, PFS, SA, S1, S2, G1, PF1, G2, P1, PF2 and A were categorised as high strength mortars to be used for structural repairs. Mix P2, having a low compressive strength is to be used as a cosmetic repair mortar. Furthermore, it was observed that a high compressive and tensile strength of the overlay does not necessarily translate into a high bond strength. The proprietary repair mortars exhibited low permeability. A review of the EN 1504-3:2005 showed that this code does not specify important crack-determining material parameters such as elastic modulus, tensile relaxation and shrinkage despite the critical role they play in the cracking performance of repair mortars. Further research into the microstructural properties of the proprietary repair materials is recommended to give additional insights into the causes of their different physical properties. This should be combined with on-site observation and testing to identify any potentially problematic macro-scale issues associated with repair mortars, particularly in relation to moisture transmission and retention. Understanding these factors amongst others, are essential to prevent damage to repaired structures by the use of incompatible repair materials.