Two surveys were conducted by NRMCA. The first survey was a short questionnaire attempting to identify companies involved with producing HPC and those who would be willing to answer more detailed questions on processing of HPC. The second questionnaire was more elaborate and asked detailed questions about the job specifications, type of structure, materials used, and processing of HPC, as well as mix design, quality control and observations about handling, placing, curing and testing concrete. Besides being sent to the previous respondents, this questionnaire was mailed to a wider pool of producers. Overall, the surveys did not generate a significant number of responses.
The first survey triggered 48 responses and a description of 108 jobs. A summary of the types of concrete specifications is given in Table 1. All concretes but one corresponded to the definition of HPC given previously. Only 24 percent of the jobs had a specification requirement for the measurement of chloride ion permeability. The general comment was that it was difficult to meet the specification for chloride ion permeability. This is due primarily to the significant variability in the test results and because there is no adequate guidance in designing concrete mixtures and modifying the production process to obtain the specified value.
| Compressive strength MPa (ksi) | Chloride penetration 103Coulombs | w/c | ||||||||
| 41 - 55 (6 - 8) |
55 - 69 (8 - 10) |
69 - 97 (10 - 14) |
> 97 (> 14) |
3 - 2 | 2 - 0.8 | > 0.8 | 1 | 2 | 3 | 4 |
| Percent of responses | ||||||||||
| 49 | 23 | 14 | 1 | 1 | 12 | 11 | 39 | 29 | 7 | 3 |
| The total number of responses were 108 from 48 companies. Seven participants stated that they did not deliver HPC. The responses were classified for strength and chloride ion permeability as described on Table 2. The w/c were divided in 4 categories: | ||||||||||
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1 = 0.40 - 0.35 2 = 0.35 - 0.30 3 = 0.30 - 0.27 4 = < 0.27 | ||||||||||
| Most of the percents were defined by the compressive strength (22 percent) or by the w/c (16 percent), or both (63 percent). Therefore, it can be deduced that the only test of durability that was considered is not always performed and that the two parameters recorded are strength and w/c. | ||||||||||
The second questionnaire yielded 24 responses from 17 companies. A summary of the concrete specifications is given in Table 2. The general conclusions are:
This second questionnaire, more extensive, was divided into three main sections: workability, finishability and curing. This article will examine these three properties in detail, combining findings from the survey and the literature.
| Compressive strength MPa (ksi) | Chloride penetration 103 Coulombs | w/c* | ||||||||
| 41 - 55 (6 - 8) | 55 - 69 (8 - 10) | 69-97 (10 - 14) | > 97 ( > 14) |
3 - 2 | 2 - 0.8 | < 0.8 | 1 | 2 | 3 | 4 |
| Percent of responses | ||||||||||
| 59 | 32 | 9 | 0 | 0 | 18 | 4 | 59 | 23 | 4 | 14 |
| There were 24 responses from 17 companies. The same
classification was adopted for the second survey as for the first. Some other characteristics are:
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| *See Table 1 for w/c categories. | ||||||||||