Built-in Concretes Made with Gypsum Free Cements: Compression Strength Determination Using Nondestructive Testing Methods

摘要

Gypsum free cement (GFC) concretes feature high initial strength within 1 to 3 days; whereas, such strength is comparable to common concrete strength after 28-days-hardening. To determine concrete strength nondestructively, ball thrust hardness tests are most frequent, in particular by Schmidt Impact Hammers, manufacturer PROCEQ Co., Switzerland. Nevertheless, ultrasonic pulse method is usable as well. To determine compression strength by means of impact hammers and to derive strength from nondestructive testing parameters, calibration correlations are described here for concretes after at least 14-days-hardening (e.g. calibration correlations of impact hammer by manufacturer or according to CSN 731373). However, when using GFC concretes, it is important to know their strength during initial hardening (1 to 3 days). This paper describes calibration correlations for GFC concretes relating to Schmidt Impact Hammers, types N and L as compared with calibration correlations defined by CSN 731373 and calibration correlations indicated by impact hammer manufacturer in question. Furthermore, another calibration correlation for compression strength determination is indicated herein on the basis of ultrasonic pulse velocity, though its practicability is rather limited, as ultrasonic pulse velocity is affected by concrete components.