FPrimeC Solutions was engaged by SNC-Lavalin Nuclear  and Aecon Industrial to perform non-destructive testing for evaluation of in-place concrete strength in concrete slab (400 sq.m). The main objective of the project was to verify the low break values from laboratory, in a limited timed, and with minimum intrusive tests possible. The structure was part of Darlington Refurbishment project by Ontario Power Generation (OPG) at the Darlington generating facilities.

    The Problem

    The client was concerned about the quality and strength of a recently poured concrete that was subject to cold weather condition. There was a concern that low and freezing temperatures might have affected the strength development is early age, and that the concrete wouldn’t reach the minimum specified strength (set by designer and regulator). The client required that the investigation be limited to non-destructive evaluation (at stage 1), and be verified with a minimum number of compressive tests on concrete cores (at stage 2), and identify potential weak points over the deck slab.

    The Solution – Estimating In-Place Concrete Strength 

    After careful review of existing data, FPrimeC designed a NDT/NDE plan for estimating in-place concrete strength in concrete slab (6″ thick). The test area was tested on a systematic grid layout, with dense spacing around the edges and shorings, and wider spacing in the interior parts of the salb. At each test location, two NDT tests were performed:

    Both tests were performed according to the standard test procedures. Rebound hammer test was conduced in accordance with the ASTM C805, whereas Ultrasonic Pulse Velocity was performed according to the ASTM C 597. In  order to identify potential weak points, and predict the compressive strength of concrete, the results of the two tests were combined into a mathematical model. Strength variation over the concrete slab was presented as a 2D contour plot, where areas with potentially low strength were identified and reported for further inspection and strengthening.

    Sample – How NDT methods for estimating in-place concrete strength in concrete slab are presented on a concrete slab.