Browsing by Author "Moffatt, Edward"

Now showing 1 - 5 of 5
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    A new performance test for evaluating the ASR potential of job mixtures
    (University of New Brunswick, 2018) Laskey, Michael J.; Thomas, Michael; Moffatt, Edward
    Alkali-silica reaction (ASR) is a problem that plagues many concrete structures worldwide, from dams to residential structures. At the moment, standardized are testing methodologies encounter problems such as leaching of alkalis, extensive testing time, or the inability to test “job-mixtures”. The University of New Brunswick concrete cylinder test (UNBCCT) was developed to overcome such difficulties through the storage of concrete samples in alkali host solutions designed to negate leaching, increase the storage temperature to accelerate the reaction, and the use of job mixture designs. With these modifications, cylinders were cast with various aggregate and cementitious material combinations (100% portland cement, and combinations of cement and SCMs such as fly ash, ground granulated blast furnace slag, and silica fume) to the dimensions of 145 mm in diameter by 285 mm in height. The cylinders were stored in containers (150mm by 300 mm in height) filled with a host solution matching the alkalinity of the concrete pore-solution. The samples were then stored in either 38°C or 60°C to determine if an accelerated version of the test was plausible. The resulting expansion was periodically measured and compared to other test methods such as the concrete prism test (CPT) and long-term exposure blocks. Alkali-leaching occurrence was also investigated through the casting of non-reactive limestone samples. These samples were periodically tested for alkali contents in a profile from the center to the surface. These profiles were generated by dissolving milled powder via hydrochloric acid or water, and measuring alkalis by inductively coupled plasma mass spectrometry (ICP-MS). Testing was also conducted on pore-solution extracted from the concrete and the host solution. The results to date indicate that the storage conditions used in the UNBCCT minimize the reduction or enrichment of alkalis in the test specimen, and that the expansion results compare well with the behavior of long-term exposure blocks. The test appears to have promise as a performance test for “job mixtures”, although further studies are required with a wider range of mixes.
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    Corrosion of reinforcing steel in concrete: monitoring techniques and mitigation strategies
    (University of New Brunswick, 2018) Fahim, Andrew; Thomas, Michael; Moffatt, Edward
    Corrosion of reinforcing steel is the most prominent cause of premature concrete deterioration. This necessitates understanding the methods available to monitor the rate of corrosion propagation, as well as the strategies that can be used to delay corrosion-induced deterioration. This thesis presents results of a study conducted to determine the reliability of several electrochemical corrosion-monitoring techniques. The reliability of these techniques was investigated experimentally, through laboratory experiments, as well as numerically, through finite element modeling. This thesis also presents results from a study on the corrosion-resistance of concrete incorporating supplementary cementing materials (SCMs) subjected to a marine environment for 25 years. This investigation included determining the effect of SCM incorporation on chloride diffusion, concrete resistivity and reinforcement corrosion rate. Finally, this thesis presents results from an investigation conducted on the performance of several corrosion-resistant reinforcements. This was performed through laboratory and field-exposure experiments implemented to compare the performance of these reinforcements to accepted standards.
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    Durability of rapid-set (ettringite-based) concrete
    (University of New Brunswick, 2016) Moffatt, Edward; Thomas, Michael
    Rapid-set concretes are currently used to repair structures such as bridge decks, substructure elements on bridges (e.g. piers and columns), pavements, and components of buildings. As the name implies, rapid-set concrete results in a high strength in a short period of time (e.g. ≥ 20 MPa in 3 hours) in order to minimize construction times and disruption to the travelling public. Although they are capable of reaching a high-early strength, they are not only meant to be a short-term solution but to survive the life of the structure. Unlike ordinary Portland cement (PC) based systems, where ettringite (C3A·3C$·H32) is a minor constituent, the hydrates in rapid-set concrete systems are primarily composed of ettringite, which forms within the first few hours of hydration. The formation of ettringite is achieved through the use of cementitious systems that are rich in calcium and aluminum bearing oxides, which include binders that contain calcium aluminate cement (CAC) or calcium sulfoaluminate cement (C$A), together with calcium sulfate (C$). High-early strength Portland cement (HEPC) with high doses of set accelerator and calcium sulfoaluminate cements (C$A) are currently being used in rapid-repair products, however, there exists limited information concerning their long-term durability in aggressive conditions often encountered in service. A new rapid setting concrete composed of a ternary blend (PC-CAC-C$) of Portland cement (PC), calcium aluminate cement (CAC), and calcium sulfate (C$) has been developed and is expected to achieve both mechanical and durability characteristics similar to that of concrete produced with either HEPC or C$A cement. This dissertation presents mechanical and durability performance data, from both laboratory and field studies, of ettringite systems based on the new ternary cement (PCCAC-C$) and two commercially-available cements that utilize calcium-sulfo-aluminate (C$A) cement. As a comparison, the performance was compared to that of portland cement based systems including high-early strength portland cement. The effect of carbonation on both the mechanical and durability properties of the various systems was also studied to determine the stability of ettringite under various environments. The use of X-ray diffraction (XRD) and scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) was used to investigate the microstructural properties. In addition to studying the durability performance of these systems, modifications were made to an existing chloride-penetration model to allow for the impact of carbonation on chloride ingress to be assessed. This included making adjustments for the changes in the physical (pore-structure) and chemical (chloride binding) resistance to chlorides.
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    Investigation of mechanical properties of expanded polystyrene low-density fibre-reinforced concrete made with different fibre types
    (University of New Brunswick, 2018) Ibeawuchi, John Chimaobi; Lloyd, Alan; Moffatt, Edward
    Fibre reinforced and low-density concrete have become popular in the construction industry today. In order for a combination of both materials to be widely accepted for use in design, a good understanding of their behaviour is needed. This study presents an experimental investigation to determine the effects of polypropylene and hooked-end steel fibres on the behaviour of low-density concrete made with expanded polystyrene beads. Digital image correlation (DIC) was used to measure displacements and strains as opposed to conventional methods of using LVDT and strain gauges and was validated as a better alternative. Crack initiation and propagation were also monitored using the DIC technique. To further understand the behaviour of both fibre types, cross-sectional analysis was carried out on a cracked section and results show steel fibres provide better resistance to cracking and improved mechanical properties than polypropylene fibres. An existing model was used to further show the behaviour of the specimens in tension.
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    Pozzolans: reactivity test method development and durability performance
    (University of New Brunswick, 2019) Kasaniya, Mahipal; Thomas, Michael; Moffatt, Edward
    It is well understood that partial replacement of portland cement with pozzolans generated as industrial by-products, such as fly ash and silica fume, have advantageous implications on the long-term performance of concrete. However, the production of the most widely available and exploited pozzolan, fly ash, is predicted to substantially decrease in the future due to the termination of coal-fired power stations around the globe. Therefore, it is crucial to explore pozzolans such as natural pozzolans and ground glasses to meet the burgeoning demand for sustainable cementitious materials. It is of a great significance to precisely assess the reactivity of pozzolans before using in major applications in the construction industry. The existing reactivity tests: strength activity index (ASTM C311/618) and lime-reactivity (CSA A30004 E1) are unreliable in evaluating pozzolans because of either inconsistent or inadequate mixture proportions. The Canadian standard test based on lime-reactivity, CSA A30004-E1, was modified by investigating four mixture designs comprising of combinations of pozzolan, portlandite (hydrated lime), calcite, and either alkaline or sulphate solution. Thermogravimetric analysis (TGA) and compressive strength tests were performed to determine the optimum portlandite proportion. The mixture design resulting in the highest compressive strength in mortars and bound water in pastes was used to establish the highest degree of the reactivity of pozzolans. This mixture design was further tested by modifying the curing regime: solution, temperature and duration. A broad-range of cementitious materials including industrial by-products, natural pozzolans and ground glasses were investigated in concretes for compressive strength, chloride permeability and migration coefficient, electrical surface and bulk resistivity, and bulk electrical conductivity. Mortar prisms were prepared for periodic monitoring of expansion due to alkali-silica reaction and sulphate attack. The results demonstrated that a larger number of natural pozzolans and ground glasses tested have considerable potential for use in concrete considering their comparable or better performance than industrial by-products (e.g., fly ash and silica fume).