Test Method Selection Several criteria were evaluated to determine which testing procedure was most appropriate for the determination of shotcrete compressive strength in an underground environment. One must remember that. The coefficient of correlation between the Schmidt Hammer and the compressive strength is 0. Ceccoli 3 1 mean value and the standard deviation of the random variable R as 2 1 ln R 2 See More. The figures indie the random variation of the strength See More. In total, standard specimens of concrete were grouped into training examples and 20 test examples to estimate concrete compressive strength. These results from tests in both positions showed that, as expected, the readings are higher in the horizontal position.

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The coefficient of variation is defined as the standard deviation divided by the aic of all tests performed on the same concrete, expressed as a percentage.

Although there is no theoretical relationship between the surface hardness and the compressive strength of the concrete, there is a strong experimental relationship. Underground Shotcrete Quality Assessment.

Thirty-six strength levels were obtained by changing the water cement ratio the slump values were adjusted by adding more or less water-reducer or super plasticizerand by changing the age at testing. Test Method Selection Several criteria were evaluated to determine which testing procedure was most appropriate for the determination of shotcrete compressive strength in an underground environment.

Some pretesting was conducted on large concrete panels about 28 x 28 x 4 in. Each result in Column 5 is the average of tests performed on the cylinders used for the determination of the compressive strength 20 SH tests per cylinder.

## Shotcrete Solutions

Also, a low value of standard deviation indies more consistent results. According to ACIthis indicates a very good control of the within-test variation. Any relationship with a. Aic Schmidt Hammer SH measures the rebound of a hardened steel hammer that is impacted. Any relationship with a coefficient of correlation over 0. The compressive strengths were measured on 4 x 8 in. This means sci the Schmidt Hammer provides a good indication of the shotcrete compressive strength.

Statistical analysis of strength of concrete – The mean value and the standard deviation S.

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In total, standard specimens of concrete were grouped into training examples and 20 test examples to estimate concrete compressive strength. This procedure involved extensive use of the SH to rapidly identify any potential poor quality shotcrete. Troetti 2 and C. Checklist for site works. Several criteria were evaluated to determine which testing procedure was most appropriate for the determination of shotcrete compressive strength in an underground environment.

An evaluation of the precision of these three tests was undertaken in the laboratory and showed that the SH was more suitable than the WP and PLI methods to evaluate the compressive strength of drymix shotcrete. The Schmidt Hammer SH measures 214-777 rebound of a hardened steel hammer that is impacted on the surface of the concrete with constant energy.

# compressive strength standard deviation excel

The coefficient of correlation between the Schmidt Hammer and the compressive strength is 0. Tests on laboratory-made concrete of various mix proportions, types of cement, and ages at test indie that, for a constant degree avi control, the standard deviation within a batch is directly proportional to the mean strength of the concrete.

Concretes with compressive strengths ranging from to 14, psi 17 to 97 MPa were used cai evaluate the precision of the testing procedure. Results from SH testing can, however, be affected by several factors, including the testing position angle of the hammer with respect to verticaltype and amount of coarse aggregates, moisture content of the concrete, and surface condition of the tested area.

These criteria were separated into three categories: To represent the walls of. Some SH testing was then carried out in a mine to evaluate the suitability of this method for use in the underground 214-77.

Obtaining the rebound value The European standard EN determines the procedure for obtaining a valid rebound nuer, based on a minimum of 9 impacts and calculating a 21-477. It is important to remember that the type and content of coarse aggregate is one of the most important factors affecting Schmidt Hammer readings.

Figure 2 presents the relationship between xci average compressive strength average of five. Because of its nondestructive characteristics, this test is an ideal method to determine the in-place quality of concrete or shotcrete.

## Aci 214-77 pdf

According to these considerations, the ideal test should: Table 1 presents some average test results obtained with the Type N hammer on panels in vertical downward and horizontal positions, respectively. The low COV of wci in-test variation 8. Because the COV is somewhat high, it takes several readings to get a good average measurement; a group of 20 readings can be considered as a good number for underground measurement.