1.0.1 This Specification is formulated with a view to promoting the development of the concrete strength testing technology with drilled core and to improving the reliability of testing results.
1.0.2 This Specification is applicable to testing the strength of ordinary concrete with strength no larger than 80MPa in the structure by using drilled cores.
1.0.3 In addition to those specified in this Specification, the testing of concrete strength with drilled core still shall comply with those specified in the current relevant standards of the nation.
2 Terms and Symbols
2.1 Terms
2.1.1 compressive strength of concrete
It is the compressive strength of structural concrete within the testing age that is equivalent to the test cube with side length of 150mm, and it is obtained by using the core specimens;
2.1.2 Estimated strength of concrete
The estimated value of the 0.05 tantile in the distribution of the compressive strength of such structural concrete within the testing age and being equivalent to the test cube with side length of 150mm.
2.1.3 Confidence level
It is the probability that the true value of the tested quantity falls into a certain interval.
2.1.4 Estimate interval
It is the range that the true value of the tested quantity falls at the set confidence level. This range is defined by using the upper limit value and lower limit value that are used for the strength estimation.
2.1.5 Standard core specimen
It is the concrete cylinder specimen of which the drilled core quality meets the requirements, the nominal diameter is 100mm and the height-diameter ratio is 1:1.
2.1.6 Inspection lot
It means a certain quantity of specimens that are produced under the same concrete strength registration, production technology, raw materials, mix proportion, forming technology and curing conditions and are submitted for testing.
2.1.7 Draw an item at random
It means drawing any one individual from the inspection lot randomly and equiprobably.
2.2 Symbols
A——the cross-sectional area of core specimen;
F——the maximum testing force obtained upon the core specimen test;
H——the height of compressive core specimen;
Scor——the standard deviation of the strength samples of core specimen;
D——the average diameter of core specimens;
——the conversion value of compressive strength of concret obtained by using indirect methods;
fcu.e——the estimated strength of concrete;
fcu,cor——the compressive strength of concrete of the core specimen;
fcu,e1——the estimated upper limit value of the compressive strength of concrete;
fcu,e2——the estimated lower limit value of the compressive strength of concrete;
k1, k2——the upper and lower limit coefficients of estimate interval;
△f——the correction quantity;
3 Strength Test
3.1 General Requirements
3.1.1 The concrete cores drilled from the structure shall be processed into the core specimens that meet the requirements.
3.1.2 The concrete strength of the core specimen shall be determined by the test method of applying acting force onto the core specimen.
3.1.3 In the compression test, the core test should use the standard core specimens of which the nominal diameter should not be less than three times of the maximum grain size of aggregates; besides, the minor-diameter core specimens may also be adopted, however, their nominal diameter shall neither be less than 70mm nor be less than two times of the maximum grain size of aggregates.
3.1.4 The core drilling method may be used for determining the estimated strength of concrete of one inspection lot or one individual member; and it may also be used for the drilled core correction method to correct the conversion value of the compressive strength of concrete that is obtained by the indirect strength test methods.
3.1.5 The tensile strength of concrete of the core specimens may be tested according to Appendix A.
