Browsing by Author "Buys, Christiaan Ernst"

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    Investigation of a practical application of the maturity method to estimate the early-age strength of concrete
    (Stellenbosch : Stellenbosch University, 2019-12) Buys, Christiaan Ernst; Wium, Jan; Jurgens, Chris
    ENGLISH ABSTRACT: This study investigates the accuracy of the Maturity Method to estimate the early-age strength of concrete in a South African context towards the possible optimization of formwork removal of suspended slabs. The Maturity Method estimates the strength of concrete based on its temperature history. Temperature measurements of concrete cubes are taken, with the maturity calculated from the temperature history. The maturity is then correlated with compressive strengths through cube compression tests at various ages to develop a mix calibration. The in-situ strength estimation is done by measuring the in-situ temperature history, and consequently maturity, and calculating the strength based on the maturity. The in-situ temperature measurement is done with newly developed wireless sensors called SmartRocks. SmartRocks are cast into concrete and measures the temperature history of concrete and transmits the data via Bluetooth to an application on a smartphone, with the maturity calculated and strength estimated by the application. The maturity can be calculated with various maturity functions. Two maturity functions that were investigated in this study, are the Nurse-Saul and Arrhenius maturity functions. From the Laboratory Test Phase that was conducted in this study, it can be concluded that the Nurse-Saul maturity function is the easiest to apply, with sufficient accuracy. The Nurse-Saul maturity function requires a Datum Temperature as input. Values for the Datum Temperature can be obtained from literature, or it can be experimentally determined. Sets of cubes were cured at three temperatures with Strength-Maturity relationships developed for these temperatures. By comparing these relationships with each other, it can be concluded that the Maturity Method is sufficiently accurate to predict in-situ concrete strength. Different strength prediction models were also investigated in this study. These models were the logarithmic, hyperbolic and exponential models respectively. It is recommended that the exponential model be used to predict the Strength-Maturity relationship. During the Site Test Phase, SmartRock sensors were cast into a slab on the construction site of an 11-storey residential development. A series of best practice guidelines for the use of SmartRocks on site is given. Two sensors were cast into the slab at the same position, in plan, at the top and bottom of slab to determine whether different maturities are developed. There was no significant difference between the maturities developed at the top and bottom of the slab. Interviews were conducted with industry professionals to determine the applicability of SmartRocks in the South African construction industry. A few major conclusions can be made from the interviews with the industry professionals. Current techniques used for in-situ strength estimation are lacking. The majority of the industry professionals also feel that the concrete suppliers should be responsible for mix calibration and that the required skills to implement SmartRocks are available in the South African construction industry.