ISO 1920-4:2020 Testing of concrete — Part 4: Strength of hardened concrete

ISO 1920-4:2020 Testing of concrete — Part 4: Strength of hardened concrete. 5.4 Apparatus The test shall be carried out using the following: 5.4.1 Compression-testing machine, robust, related to the size of specimen and capable of providing the rate of loading with minimum desired specifications in £4 and 5S. It shall be in calibration at the time of test. The calibration shall be carried out at least once per year. Accuracy of the test machine shall be such that the percentage error for the loads within proposed range of use of the machine and shall not exceed ±1,0 % of the indicated load. The compression testing machine shall he provided with a control system. The control system may be operated either by manual or automatic means. If the machine is not equipped with automatic application of force, a pacer shall be fitted to enable the operator to maintain the specified rate. The pacer shall indicate a rate within ±5,0 % of the specified rate. 5.4.2 Machine platens and auxiliary platens, with a hardness value of at least 550 I-TV (Vickers Hardness). The thickness of the auxiliary platens shall heat least 23 mm. The roughness value, Ra, for the surface texture of the contact faces of the auxiliary platen shall be between 0,4 pm and 3,2 pm. 5.5 Force application The device for applying loads shall consist of two upper rollers and two lower rollers (see FiguxeS). All rollers shall be manufactured from steel and shall have a circular cross-section with a diameter between 20 mm and 40 mm and shall be at least 10 mm longer than the width of the test specimen. Each roller, except one of the lower ones, shall be capable of rotating around its axis and of being inclined in a plane normal to the longitudinal axis of the test specimen. The distance, Lroi, between the lower (outer) rollers (i.e. the span) shall be equal to 3!, where I is the width of the specimen. The distance between the upper (inner) rollers shall be equal to I. The inner rollers shall be equally spaced between the outer rollers as shown in Figure 5. All rollers shall be adjusted in the positions illustrated in Figi.ire5 to an accuracy of ±2 mm. 5.6.1 Preparation and positioning of specimens The specimen shall be examined and any abnormalities shall be reported. For specimens stored in water, excess moisture shall be...