1、8.1 GENERAL 8.1.1 Description Section 8 CONCRETE STRUCTURES This work shall consist of furnishing, placing, finishing, and curing concrete in bridges, culverts, and miscellaneous structures in accordance with these specifications and conforming to the lines, grades, and dimensions shown on the plans
2、. The work includes elements of structures constructed by cast-in-place and precast methods using either plain (unreinforced), reinforced, or prestressed concrete or any combination thereof. The requirements of this section are not applica- ble to precast box culvert structures, which are addressed
3、in Section 27. quate arrangements will be provided for curing, finishing, and protecting the concrete. 8.2 CLASSES OF CONCRETE 8.2.1 General The class of concrete to be used in each part of the structure shall be as specified or shown on the plans. If not shown or specified, the Engineer will design
4、ate the class of concrete to be used. 8.2.2 Normal Weight Concrete Eight classes of normal weight concrete are provided for in these Specifications as listed in Table 8.2. 8.1.2 Related Work 8.2.3 Lightweight Concrete Other work involved in the construction of concrete structures shall be as specifi
5、ed in the applicable sections of this Specification. Especially applicable are Section 3 for forms and falsework, Section 9 for reinforcing steel, and Section 10 for prestressing. Lightweight concrete shall conform to the require- ments specified in the special provisions or shown on the plans. When
6、 the special provisions require the use of nat- ural sand for a portion or all of the fine aggregate, the nat- ural sand shall conform to AASHTO M 6. 8.1.3 Construction Methods 8.3 MATERIALS Whenever the specifications permit the Contractor to select the method or equipment to be used for any operat
7、ion, it shall be the Contractors responsibility to employ methods and equipment which will produce satisfactory work under the conditions encountered and which will not damage any partially completed portions of the work. Falsework and forms shall conform to the require- ments of Section 3, “Tempora
8、ry Works.” Generally, all concrete shall be fully supported until the required strength and age has been reached. However, the slip form method will be permitted for the construc- tion of pier shafts and railings providing the Contractors plan assures that: (1) the results will be equal in all respe
9、ct to those obtained by the use of fixed forms, and (2) ade- 8.3.1 Cements Portland cements shall conform to the requirements of AASHTO M 85 (ASTM C 150) and Blended Hydraulic cements shall conform to the requirements of AASHTO M 240 (ASTM C 595). For Type 1PPortland-pozzolan ce- ment, the pozzolan
10、constituent shall not exceed 20% of the weight of the blend and the loss on ignition of the poz- zolan shall not exceed 5%. Unless otherwise specified, only Type I, II, or III Port- land Cement, Spes IA, IIA, or IIIAAir Entrained Portland Cement, or Types IP or IS Blended Hydraulic cements shall be
11、used. Types IA, IIA, and IIIA cements may be used only in concrete where air entrainment is required. 525 526 HIGHWAY BRIDGES 8.3.1 TABLE 8.2 Specified Minimum Maximum Air Size of Coarse Compressive Cement WaterICement Content Aggregate Strength Content Ratio Range Per AASHTO M 43 (28 Days) Class of
12、 Pounds Concrete Per CY Lbs Per Lb Percent Square Openings (lb /in. *) 61 1 61 1 517 517 658 65 8 564 658 0.49“ 0.45 0.58 0.55 0.49 0.45 0.49“ 0.58 - 6- 1-1/2 - 5-c 1-1/2 - 7-c 1-1/2 As specified elsewhere - 1 in. to No. 4 1 in. to No. 4 2 in. to No. 3 and 1 in. to No. 4b 2 in. to No. 3 and 1 in. to
13、 No. 4b 1/2 in. to No. 4 1/2 in. to No. 4 1 in. to No. 4 or 3/4 in. to No. 4 1 in. to No. 4 4,000 4,000 2,400 2,400 4,000 4,000 As specified elsewhere - a For concrete in or over saltwater or exposed to deicing chemicals, the maximum waterkement ratio shall be 0.45. Coarse Aggregate for Class B and
14、Class B(AE) shall be furnished in two separate sizes as shown. Low-alkali cements conforming to the requirements of AASHTO M 85 for low-alkali cement shall be used when specified or when ordered by the Engineer as a condition of use for aggregates of limited alkali-silica reactivity. Unless otherwis
15、e permitted, the product of only one mill of any one brand and type of cement shall be used for like elements of a structure that are exposed to view, except when cements must be blended for reduction of any exces- sive air-entrainment where air-entraining cement is used. 8.3.2 Water Water used in m
16、ixing and curing of concrete shall be subject to approval and shall be reasonably clean and free of oil, salt, acid, alkali, sugar, vegetable, or other injurious substances. Water will be tested in accordance with, and shall meet the suggested requirements of AASHTO T 26. Water known to be of potabl
17、e quality may be used with- out test. Where the source of water is relatively shallow, the intake shall be so enclosed as to exclude silt, mud, grass, or other foreign materials. Mixing water for concrete in which steel is embedded shall not contain a chloride ion concentration in excess of 1,000 pp
18、m or sulphates as SO4 in excess of 1,300 ppm. 8.3.3 Fine Aggregate Fine aggregate for concrete shall conform to the re- quirements of AASHTO M 6. 8.3.4 Coarse Aggregate Coarse aggregate for concrete shall conform to the re- quirements of AASHTO M 80. 8.3.5 Lightweight Aggregate Lightweight aggregate
19、 for concrete shall conform to the requirements of AASHTO M 195 (ASTM C 330). 8.3.6 Air-Entraining and Chemical Admixtures Air-entraining admixtures shall conform to the re- quirements of AASHTO M 154 (ASTM C 260). Chemical admixtures shall conform to the require- ments of AASHTO M 194 (ASTM C 494).
20、 Unless other- wise specified, only Type A (Water-reducing), Type B (Retarding), Type D (Water-reducing and retarding), Type F (Water-reducing, high range) or Type G (Water-reduc- ing, high range and retarding) shall be used. 8.3.6 DIVISION II-CONSTRUCTION 527 Admixtures containing chloride ion (Ci)
21、 in excess of 1% by weight of the admixture shall not be used in rein- forced concrete. Admixtures in excess of 0.1% shall not be used in prestressed concrete. A Certificate of Compliance signed by the manufac- turer of the admixture shall be furnished to the Engineer for each shipment of admixture
22、used in the work. Said Certificate shall be based upon laboratory test results from an approved testing facility and shall certify that the ad- mixture meets the above specifications. If more than one admixture is used, the admixtures shall be compatible with each other and shall be incorpo- rated i
23、nto the concrete mix in correct sequence so that the desired effects of all admixtures are obtained. Air-entraining and chemical admixtures shall be incor- porated into the concrete mix in a water solution. The water so included shall be considered to be a portion of the allowed mixing water. For no
24、rmal weight concrete the absolute volume method, such as described in American Concrete Institute Publication 211.1, shall be used in selecting mix propor- tions. For structural lightweight concrete, the mix propor- tions shall be selected on the basis of trial mixes with the cement factor rather th
25、an the waterkement ratio being de- termined by the specified strength using methods such as those described in American Concrete Institute Publica- tion 211.2. The mix design shall be based upon obtaining an aver- age concrete strength sufficiently above the specified strength so that, considering t
26、he expected variability of the concrete and test procedures, no more than 1 in 10 strength tests will be expected to fall below the specified strength. Mix designs shall be modified during the course of the work when necessary to ensure compliance with strength and consistency requirements. 8.4.1.2
27、Trial Batch Tests 8.3.7 Mineral Admixtures Fly ash pozzolans and calcined natural pozzolans for use as mineral admixtures in concrete shall conform to the requirements of AASHTO M 295 (ASTM C 61 8). The use of fly ash as produced by plants that utilize the limestone injection process or use compound
28、s of sodium, ammonium or sulphur, such as soda ash, to control stack emissions shall not be used in concrete. A Certificate of Compliance, based on test results and signed by the producer of the mineral admixture certify- ing that the material conforms to the above specifications, shall be furnished
29、 for each shipment used in the work. 8.3.8 Steel Materials and installation of reinforcing and pre- stressing steel shall conform to the requirements of Sections 9, “Reinforcing Steel,” and 10, “Prestressing,” respectively. For classes A, A(AE) and P concrete, for lightweight concrete, and for other
30、 classes of concrete when specified or ordered by the Engineer, satisfactory performance of the proposed mix design shall be verified by laboratory tests on trial batches. The results of such tests shall be furnished to the Engineer by the Contractor or the manufacturer of precast elements at the ti
31、me the proposed mix design is submitted. For mix design approval, the strengths of a min- imum of five test cylinders taken from a trial batch shall average at least 800 psi greater than the specified strength. If materials and a mix design identical to those pro- posed for use have been used on oth
32、er work within the previous year, certified copies of concrete test results from this work which indicate full compliance with these spec- ifications may be substituted for such laboratory tests. If the results of more than 10 such strength tests are avail- able from historical records for the past
33、year, average strength for these tests shall be at least 1.28 standard de- viations above the specified strength. 8.4.1.3 Approval 8.4 PROPORTIONING OF CONCRETE 8.4.1 Mix Design 8.4.1.1 Responsibility and Criteria The Contractor shall design and be responsible for the performance of all concrete mix
34、es used in structures. The mix proportions selected shall produce concrete that is sufficiently workable and finishable for all uses intended and shall conform to the requirements in Table 8.2 and all other requirements of this section. All mix designs, and any modifications thereto, shall be approv
35、ed by the Engineer prior to use. Mix design data provided to the Engineer for each class of concrete re- quired shall include the name, source, type, and brand of each of the materials proposed for use and the quantity to be used per cubic yard of concrete. 8.4.2 Water Content For calculating the wa
36、terkement ratio of the mix, the weight of the water shall be that of the total free water in 528 HIGHWAY BRIDGES 8.4.2 the mix which includes the mixing water, the water in any admixture solutions and any water in the aggregates in ex- cess of that needed to reach a saturated-surface-dry con- dition
37、. The amount of water used shall not exceed the limits listed in Table 8.2 and shall be further reduced as neces- sary to produce concrete of the consistencies listed in Table 8.3 at the time of placement: TABLE 8.3 Nominal Maximum Slump Slump npe of Work Inches Inches Formed Elements: Sections Over
38、 12 in. Thick 1-3 5 Sections 12 in. Thick or Less 1-4 5 Cast-in-place Piles and Drilled Shafts not Vibrated 5-8 9 Concrete Placed Under Water 5-8 9 Filling for Rip-rap 3-7 8 When Type F or G high range water reducing admix- tures are used, the above listed slump limits may be ex- ceeded as permitted
39、 by the Engineer. When the consistency of the concrete is found to ex- ceed the nominal slump, the mixture of subsequent batches shall be adjusted to reduce the slump to a value within the nominal range. Batches of concrete with a slump exceeding the maximum specified shall not be used in the work.
40、If concrete of adequate workability cannot be obtained by the use of the minimum cement content allowed, the cement and water content shall be increased without ex- ceeding the specified waterkement ratio, or an approved admixture shall be used. 8.4.3 Cement Content The minimum cement content shall
41、be as listed in Table 8.2 or otherwise specified. The maximum cement or cement plus minerai admixture content shall not exceed 800 pounds per cubic yard of concrete. The actual cement content used shall be within these limits and shall be suf- ficient to produce concrete of the required strength and
42、 consistency. 8.4.4 Mineral Admixtures Mineral admixtures shall be used in the amounts spec- ified. In addition, when either Qpes I, II, IV, or V (AASHTO M 85) cements are used and mineral admix- tures are neither specified nor prohibited, the Contractor will be permitted to replace up to 20% of the
43、 required Port- land cement with a mineral admixture. The weight of the mineral admixture used shall be equal to or greater than the weight of the Portland cement replaced. In calculating the waterkement ratio of the mix, the weight of the cement shall be considered to be the sum of the weights of t
44、he Portland cement and the mineral admixture. 8.4.5 Air-Entraining and Chemical Admixtures Air-entraining and chemical admixtures shall be used as specified. Otherwise, such admixtures may be used, at the option and expense of the Contractor when permitted by the Engineer, to increase the workabilit
45、y or alter the time of set of the concrete. 8.5 MANUFACTURE OF CONCRETE The production of ready-mixed concrete shall conform to the requirements of AASHTO M 157 (ASTM C 94) and the requirements of this Article 8.5. The production of concrete with stationary mixers shall conform to the ap- plicable r
46、equirements of AASHTO M 157 (ASTM C 94) and the requirements of this article. 8.5.1 Storage of Aggregates The handling and storage of concrete aggregates shall be such as to prevent segregation or contamination with foreign materials. The methods used shall provide for ad- equate drainage so that th
47、e moisture content of the aggre- gates is uniform at the time of batching. Different sizes of aggregate shall be stored in separate stock piles suffi- ciently removed from each other to prevent the material at the edges of the piles from becoming intermixed. When specified in Table 8.2 or in the spe
48、cial provi- sions, the coarse aggregate shall be separated into two or more sizes in order to secure greater uniformity of the concrete mixture. 8.5.2 Storage of Cement The Contractor shall provide suitable means for stor- ing and protecting cement against dampness. Cement which for any reason has b
49、ecome partially set or which contains lumps of caked cement will be rejected. Cement held in storage for a period of over 3 months if bagged or 6 months if bulk, or cement which for any reason the Engineer may suspect of being damaged, shall be subject to a retest before being used in the work. 8.5.2 DIVISION II-CONSTRUCTION 529 Copies of cement records shall be furnished to the En- gineer, showing, in such detail, as he may reasonably re- quire, the quantity used during the day or run at each part of the work. 8.5.3 Measurement of Materials Materials shall be measured by weighing, except as
