1964_BUILDING_(CONSTRUCTION)_REGULATIONS — Page 119

1985 Ed.]

Building (Construction) Regulations

CAP. 123

B 119

[Subsidiary]

[reg. 1947.]

## FIRST SCHEDULE

## METHODS FOR DETERMINING THE RESISTANCE TO CRUSHING OF CONCRETE

## PART I

## GENERAL

1. (1) In this Schedule unless the contrary appears-

"average resistance to crushing" means the arithmetical mean of the resistances to crushing of a stated number of cubes;

"consecutive cubes" means cubes made from consecutive samples of concrete as taken during the work, and tested at the same age;

"designed mean resistance to crushing" means the mean resistance to crushing to be aimed for in designing a mix to comply with a specified resistance to crushing;

"designed standard deviation" is the standard deviation adopted in designing a mix;

"mean resistance to crushing" means the arithmetical mean resistance to crushing of all the concrete of a particular grade produced in a given period of time;

"preliminary test" means a test made in accordance with BS 1881: Parts 3 and 4: 1970 both prior to the commencement of the work and subsequently whenever any important change is to be made in the materials or in the proportions of the materials to be used, to ascertain the suitability of the available materials or to determine suitable mix proportions;

"range" means the difference between the highest and lowest value in a set;

"set" means a stated number of consecutive individual results;

"specified resistance to crushing" means for ordinary concretes and Quality A concretes, the resistance to crushing specified in Tables IV and V for the appropriate grade; for special mixes and designed mixes, the particular resistance to crushing within the limits of Table VI appropriate to the permissible stresses adopted for the structural design;

"standard deviation" means a measure of variability calculated from the resistances to crushing of the individual cubes tested at a given age each representing a different batch of concrete having the same specified resistance to crushing;

"works resistance to crushing" means the resistance to crushing obtained from works tests;

"works test" means a test made in accordance with BS 1881: Parts 3 and 4: 1970 during the course of the work to assess or prove the quality of the concrete used in the work.

(2) The mean resistance to crushing may be estimated from tests on such a number of cubes of concrete as may be approved by the Building Authority generally or for a particular grade of concrete or in a particular case.

(3) The standard deviation, σ, may be calculated from either of the following equations:

Interpretation.

L.N. 294/76.

L.N. 294/76.

σ = √[(Σ(x-x)2)/(n-1)] or σ = √[(Σx2 - (Σx)2/n)/(n-1)]

where σ = standard deviation;

x = individual resistance to crushing;

x = average resistance to crushing;

n = number of individual results.