Investigation of a practical application of the maturity method to estimate the early-age strength of concrete

Christiaan Ernst, Buys (2019-12)

Thesis (MEng)--Stellenbosch University, 2019.

Thesis

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.

AFRIKAANSE OPSOMMING: Hierdie studie ondersoek die akuuraatheid van die Rypheidsmetode om die vroeë-ouderdom sterkte van beton the voorspel in ‘n Suid Afrikaanse konteks, om moontlik optimisering van bekisting verwydering te bereik. Die Rypheidsmetode voorspel sterkte op grond van die beton se temperatuur geskiedenis. Die rypheid van beton word bereken van die beton se temperatuur lesings. Die rypheid word dan gekorrelleer met die druksterkte deur middel van kubus druktoetse by verskillende ouderdomme om ‘n meng kalibrasie te ontwikkel. Die voorspelling van die in-situ beton sterkte word gedoen deur die in-situ temperatuur geskiedenis, en gevolglik, die rypheid, te meet. Die sterkte word voorspel gebasseer op die in-situ rypheid. Die in-situ temperatuur meting word gedoen met nuut ontwikkelde sensors, genaamd SmartRocks. Hierdie sensors word in beton gegiet, dit meet dan die in-situ temperatuur en dra die data oor met Bluetooth tegnologie na ‘n slimfoon. Die rypheid en sterkte word met ‘n toepassing op die slimfoon bereken. Rypheid van beton kan met verskeie rypheidsfunksies bereken word. Twee rypheidsfunksies is ondersoek in hierdie studie, naamlik die Nurse-Saul – en Arrhenius rypheidsfunksies. Vanaf die laboratorium toetse wat gedoen is in hierdie studie, kan daar afgelei word dat die Nurse-Saul rypheidsfunksie die eenvoudigste is, met genoegsame akuuraatheid om toe te pas. Die Nurse-Saul rypheidsfunksie benodig ‘n Datum Temperatuur, as ‘n konstante. Waardes vir die Datum Temperatuur, kan van die literatuur verkry word, of dit kan eksperimenteel bepaal word. Kubus stelle is nabehandel by drie verkillende temperature en Sterkte-Rypheidsverhoudings is ontwikkel vir hierdie temperature. Deur hierdie verhoudinge met mekaar te vergelyk, kan daar afgelei word dat die Rypheidsmetode in-situ beton sterkte kan voorspel met genoegsame akuuraatheid. Verskillende modelle wat die Sterkte-Rypheidsverhouding voorspel, is ook ondersoek in hierdie studie. Hierdie modelle is logartimies, hiperbolies en exponensieël van aard. Dit word voorgestel om die eksponensiële model te gebruik. Gedurende die tereintoetse, is SmartRock sensors ingegiet in ‘n blad op die konstruksie terein van ‘n 11-verdieping residensiële ontwikkeling. ‘n Reeks van beste praktyke vir die gebruik van SmartRocks word nou voorgestel. Twee sensors is op dieselfde posisie, in plan, aan die bo- en onderkant van die blad gegiet, om te bepaal of daar verskille is in die rypheid wat die beton aan die bo- en onderkante ontwikkel. Daar was geen noemenswaardige verskil in die twee ryphede nie. Onderhoude is gevoer met professionele lui uit die siviel ingenieurswese industrie, om die toepaslikhied van SmartRocks in Suid Afrika te bepaal. ‘n Paar gevolgtrekkings kan gemaak word. Huidige tegnieke vir in-situ sterkte voorspelling skiet tekort en die meerderheid van die individue voel dat beton verskaffers verantwoordelik moet wees vir die meng kalibrasie. Verder, is die meerderheid van mening dat kontrakteurs oor die benodigde vaardighede beskik om die SmartRock effektiewelik toe te pas.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/107213
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