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Title: Section 1905  •  Size: 37734

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SECTION 1905 - CONCRETE QUALITY, MIXING AND PLACING

1905.0 Notations.

= specified compressive strength of concrete, psi (MPa).

= required average compressive strength of concrete used as the basis for selection of concrete proportions, psi (MPa).

= average splitting tensile strength of lightweight aggregate concrete, psi (MPa).

s = standard deviation, psi (MPa).

1905.1 General.

1905.1.1 Concrete shall be proportioned to provide an average compressive strength as prescribed in Section 1905.3.2, as well as satisfy the durability criteria of Section 1904. Concrete shall be produced to minimize frequency of strengths below as prescribed in Section 1905.6.3.

1905.1.2 Requirements for shall be based on tests of cylinders made and tested as prescribed in Section 1905.6.2.

1905.1.3 Unless otherwise specified, shall be based on 28-day tests. If other than 28 days, test age for shall be as indicated in design drawings or specifications.

Design drawings shall show specified compressive strength of concrete for which each part of structure is designed.

1905.1.4 Where design criteria in Sections 1909.5.2.3, 1911.2; and 1912.2.4.2, provide for use of a splitting tensile strength value of concrete, laboratory tests shall be made to establish value of corresponding to specified values of .

1905.1.5 Splitting tensile strength tests shall not be used as a basis for field acceptance of concrete.

1905.2 Selection of Concrete Proportions.

1905.2.1 Proportions of materials for concrete shall be established to provide:

1. Workability and consistency to permit concrete to be worked readily into forms and around reinforcement under conditions of placement to be employed without segregation or excessive bleeding.

2. Resistance to special exposures as required by Section 1904.

3. Conformance with strength test requirements of Section 1905.6.

1905.2.2 Where different materials are to be used for different portions of proposed work, each combination shall be evaluated.

1905.2.3 Concrete proportions, including water-cementitious materials ratio, shall be established on the basis of field experience and/or trial mixtures with materials to be employed, except as permitted in Section 1905.4 or required by Section 1904.

1905.3 Proportioning on the Basis of Field Experience and Trial Mixtures.

1905.3.1 Standard deviation.

1905.3.1.1 Where a concrete production facility has test records, a standard deviation shall be established. Test records from which a standard deviation is calculated:

1. Must represent materials, quality control procedures and conditions similar to those expected, and changes in materials and proportions within the test records shall not have been more restricted than those for proposed work.

2. Must represent concrete produced to meet a specified strength or strengths within 1,000 psi (6.89 MPa) of that specified for proposed work.

3. Must consist of at least 30 consecutive tests or two groups of consecutive tests totaling at least 30 tests as defined in Section 1905.6.1.4, except as provided in Section 1905.3.1.2.

1905.3.1.2 Where a concrete production facility does not have test records meeting requirements of Section 1905.3.1.1, but does have a record based on 15 to 29 consecutive tests, a standard deviation may be established as the product of the calculated standard deviation and the modification factor of Table 19-A-5. To be acceptable, the test record must meet the requirements of Section 1905.3.1.1, Items 1 and 2, and represent only a single record of consecutive tests that span a period of not less than 45 calendar days.

1905.3.2 Required average strength.

1905.3.2.1 Required average compressive strength used as the basis for selection of concrete proportions shall be the larger of Formula (5-1) or (5-2) using a standard deviation calculated in accordance with Section 1905.3.1.1 or 1905.3.1.2.
(5-1)

or
(5-2)


For SI:

1905.3.2.2 When a concrete production facility does not have field strength test records for calculation of standard deviation meeting requirements of Section 1905.3.1.1 or 1905.3.1.2, required average strength shall be determined from Table 19-A-6 and documentation of average strength shall be in accordance with requirements of Section 1905.3.3.

1905.3.3 Documentation of average strength. Documentation that proposed concrete proportions will produce an average compressive strength equal to or greater than required average compressive strength may consist of a field strength test record, several strength test records, or trial mixtures.

1905.3.3.1 When test records are used to demonstrate that proposed concrete proportions will produce the required average strength , such records shall represent materials and conditions similar to those expected. Changes in materials, conditions and proportions within the test records shall not have been more restricted than those for proposed work. For the purpose of documenting average strength potential, test records consisting of less than 30 but not less than 10 consecutive tests may be used, provided test records encompass a period of time not less than 45 days. Required concrete proportions may be established by interpolation between the strengths and proportions of two or more test records each of which meets other requirements of this section.

1905.3.3.2 When an acceptable record of field test results is not available, concrete proportions may be established based on trial mixtures meeting the following restrictions:

1. Combination of materials shall be those for proposed work.

2. Trial mixtures having proportions and consistencies required for proposed work shall be made using at least three different water-cementitious materials ratios or cementitious materials contents that will produce a range of strengths encompassing the required average strength .

3. Trial mixture shall be designed to produce a slump within ± 0.75 inch (± 19 mm) of maximum permitted, and for air-entrained concrete, within ± 0.5 percent of maximum allowable air content.

4. For each water-cementitious materials ratio or cementitious materials content, at least three test cylinders for each test age shall be made and cured. Cylinders shall be tested at 28 days or at test age designated for determination of .

5. From results of cylinder tests, a curve shall be plotted showing relationship between water-cementitious materials ratio or cementitious materials content and compressive strength at designated test age.

6. Maximum water-cementitious materials ratio or minimum cementitious materials content for concrete to be used in proposed work shall be that shown by the curve to produce the average strength required by Section 1905.3.2, unless a lower water-cementitious materials ratio or higher strength is required by Section 1904.

1905.4 Proportioning by Water-Cementitious Materials Ratio.

1905.4.1 If data required by Section 1905.3 are not available, concrete proportions shall be based on water-cementitious materials ratio limits in Table 19-A-7, if approved by the building official.

1905.4.2 Table 19-A-7 shall be used only for concrete to be made with cements meeting strength requirements for Type I, I-A, II, II-A, III, III-A or V; or Type IS, IS-A, IS(MS), IS-A(MS), I(SM), I(SM)-A, IP, IP-A, I(PM), I(PM)-A, IP(MS), IP-A(MS), or P of U.B.C. Standard 19-1, and shall not be applied to concrete containing lightweight aggregates or admixtures other than those for entraining air.

1905.4.3 Concrete proportioned by water-cementitious materials ratio limits prescribed in Table 19-A-7 shall also conform to special exposure requirements of Section 1904 and to compressive strength test criteria of Section 1905.6.

1905.5 Average Strength Reduction. As data become available during construction, amount by which value of must exceed specified value of may be reduced, provided:

1. Thirty or more test results are available and average of test results exceeds that required by Section 1905.3.2.1, using a standard deviation calculated in accordance with Section 1905.3.1.1, or

2. Fifteen to 29 test results are available and average of test results exceeds that required by Section 1905.3.2.1, using a standard deviation calculated in accordance with Section 1905.3.1.1, and

3. Special exposure requirements of Section 1904 are met.

1905.6 Evaluation and Acceptance of Concrete.

1905.6.1 Frequency of testing.

1905.6.1.1 Samples for strength tests of each class of concrete placed each day shall be taken not less than once a day, or not less than once for each 150 cubic yards (115 ) of concrete, or not less than once for each 5,000 square feet (465 ) of surface area for slabs or walls.

1905.6.1.2 On a given project, if the total volume of concrete is such that the frequency of testing required by Section 1905.6.1.1 above would provide less than five strength tests for a given class of concrete, tests shall be made from at least five randomly selected batches or from each batch if fewer than five batches are used.

1905.6.1.3 When total quantity of a given class of concrete is less than 50 cubic yards (38 ), strength tests are not required when evidence of satisfactory strength is submitted to and approved by the building official.

1905.6.1.4 A strength test shall be the average of the strengths of two cylinders made from the same sample of concrete and tested at 28 days or at test age designated for determination of .

1905.6.2 Laboratory-cured specimens.

1905.6.2.1 Samples for strength tests shall be taken.

1905.6.2.2 Cylinders for strength tests shall be molded and laboratory cured and tested.

1905.6.2.3 Strength level of an individual class of concrete shall be considered satisfactory if both the following requirements are met:

1. Average of all sets of three consecutive strength tests equal or exceed .

2. No individual strength test (average of two cylinders) falls below by more than 500 psi (3.45 MPa).

1905.6.2.4 If either of the requirements of Section 1905.6.2.4 are not met, steps shall be taken to increase the average of subsequent strength test results. Requirements of Section 1905.6.4 shall be observed if requirement of Section 1905.6.2.3 is not met.

1905.6.3 Field-cured specimens.

1905.6.3.1 The building official may require strength tests of cylinders cured under field conditions to check adequacy of curing and protection of concrete in the structure.

1905.6.3.2 Field-cured cylinders shall be cured under field conditions, in accordance with Section 1903.8.

1905.6.3.3 Field-cured test cylinders shall be molded at the same time and from the same samples as laboratory-cured test cylinders.

1905.6.3.4 Procedures for protecting and curing concrete shall be improved when strength of field-cured cylinders at test age designated for determination of is less than 85 percent of that of companion laboratory-cured cylinders. The 85 percent limitation shall not apply if field-cured strength exceeds by more than 500 psi (3.45 MPa).

1905.6.4 Investigation of low-strength test results.

1905.6.4.1 If any strength test of laboratory-cured cylinders falls below specified value of by more than 500 psi (3.45 MPa) or if tests of field-cured cylinders indicate deficiencies in protection and curing, steps shall be taken to assure that load-carrying capacity of the structure is not jeopardized.

1905.6.4.2 If the likelihood of low-strength concrete is confirmed and computations indicate that load-carrying capacity may have been significantly reduced, tests of cores drilled from the area in question may be required. In such case, three cores shall be taken for each strength test more than 500 psi (3.45 MPa) below specified value of .

1905.6.4.3 If concrete in the structure will be dry under service conditions, cores shall be air dried [temperatures 60°F. to 80°F. (15.6°C. to 26.7°C.), relative humidity less than 60 percent] for seven days before test and shall be tested dry. If concrete in the structure will be more than superficially wet under service conditions, cores shall be immersed in water for at least 40 hours and be tested wet.

1905.6.4.4 Concrete in an area represented by core tests shall be considered structurally adequate if the average of three cores is equal to at least 85 percent of and if no single core is less than 75 percent of . Additional testing of cores extracted from locations represented by erratic core strength results shall be permitted.

1905.6.4.5 If criteria of Section 1905.6.4, Item 4, are not met, and if structural adequacy remains in doubt, the responsible authority may order load tests as outlined in Section 1920 for the questionable portion of the structure, or take other appropriate action.

1905.7 Preparation of Equipment and Place of Deposit.

1905.7.1 Preparation before concrete placement shall include the following:

1. All equipment for mixing and transporting concrete shall be clean.

2. All debris and ice shall be removed from spaces to be occupied by concrete.

3. Forms shall be properly coated.

4. Masonry filler units that will be in contact with concrete shall be well drenched.

5. Reinforcement shall be thoroughly clean of ice or other deleterious coatings.

6. Water shall be removed from place of deposit before concrete is placed unless a tremie is to be used or unless otherwise permitted by the building official.

7. All laitance and other unsound material shall be removed before additional concrete is placed against hardened concrete.

1905.8 Mixing.

1905.8.1 All concrete shall be mixed until there is a uniform distribution of materials and shall be discharged completely before mixer is recharged.

1905.8.2 Ready-mixed concrete shall be mixed and delivered in accordance with requirements of U.B.C. Standard 19-3.

Concrete made by the on-site volumetric batching and continuous mixing procedure shall be mixed and delivered in accordance with requirements of U.B.C. Standard 19-4.

1905.8.3 Job-mixed concrete shall be mixed in accordance with the following:

1. Mixing shall be done in a batch mixer of an approved type.

2. Mixer shall be rotated at a speed recommended by the manufacturer.

3. Mixing shall be continued for at least 11/2 minutes after all materials are in the drum, unless a shorter time is shown to be satisfactory by the mixing uniformity tests of U.B.C. Standard 19-3.

4. Materials handling, batching and mixing shall conform to applicable provisions of U.B.C. Standard 19-3.

5. A detailed record shall be kept to identify:

5.1 Number of batches produced;

5.2 Proportions of materials used;

5.3 Approximate location of final deposit in structure;

5.4 Time and date of mixing and placing.

1905.9 Conveying.

1905.9.1 Concrete shall be conveyed from mixer to place of final deposit by methods that will prevent separation or loss of materials.

1905.9.2 Conveying equipment shall be capable of providing a supply of concrete at site of placement without separation of ingredients and without interruptions sufficient to permit loss of plasticity between successive increments.

1905.10 Depositing.

1905.10.1 Concrete shall be deposited as nearly as practicable in its final position to avoid segregation due to rehandling or flowing.

1905.10.2 Concreting shall be carried on at such a rate that concrete is at all times plastic and flows readily into spaces between reinforcement.

1905.10.3 Concrete that has partially hardened or been contaminated by foreign materials shall not be deposited in the structure.

1905.10.4 Retempered concrete or concrete that has been remixed after initial set shall not be used unless approved by the building official.

1905.10.5 After concreting is started, it shall be carried on as a continuous operation until placing of a panel or section, as defined by its boundaries or predetermined joints, is completed, except as permitted or prohibited by Section 1906.4.

1905.10.6 Top surfaces of vertically formed lifts shall be generally level.

1905.10.7 When construction joints are required, joints shall be made in accordance with Section 1906.4.

1905.10.8 All concrete shall be thoroughly consolidated by suitable means during placement and shall be thoroughly worked around reinforcement and embedded fixtures and into corners of forms.

1905.11 Curing.

1905.11.1 Concrete (other than high-early-strength) shall be maintained above 50°F. (10.0°C.) and in a moist condition for at least the first seven days after placement, except when cured in accordance with Section 1905.11.3.

1905.11.2 High-early-strength concrete shall be maintained above 50°F. (10.0°C.) and in a moist condition for at least the first three days, except when cured in accordance with Section 1905.11.3.

1905.11.3 Accelerated curing.

1905.11.3.1 Curing by high-pressure steam, steam at atmospheric pressure, heat and moisture or other accepted processes, may be employed to accelerate strength gain and reduce time of curing.

1905.11.3.2 Accelerated curing shall provide a compressive strength of the concrete at the load stage considered at least equal to required design strength at that load stage.

1905.11.3.3 Curing process shall be such as to produce concrete with a durability at least equivalent to the curing method of Section 1905.11.1 or 1905.11.2.

1905.11.3.4 When required by the building official, supplementary strength tests in accordance with Section 1905.6.3 shall be performed to assure that curing is satisfactory.

1905.12 Cold Weather Requirements.

1905.12.1 Adequate equipment shall be provided for heating concrete materials and protecting concrete during freezing or near-freezing weather. All concrete materials and all reinforcement, forms, fillers and ground with which concrete is to come in contact shall be free from frost.

1905.12.2 Frozen materials or materials containing ice shall not be used.

1905.13 Hot Weather Requirements. During hot weather, proper attention shall be given to ingredients, production methods, handling, placing, protection and curing to prevent excessive concrete temperatures or water evaporation that may impair required strength or serviceability of the member or structure.

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