(A) Concrete placement.
(1) Site conditions. Before placing concrete, the contractor shall:
(a) Erect and clean all formwork and reinforcement;
(b) Prevent groupings of conduits, pipes and sleeves in concrete that would significantly impair the strength of the concrete;
(c) Install all items to be embedded in concrete. Position accurately and secure against displacement. Do not embed aluminum items in concrete;
(d) Remove all wood scraps, ice, snow, frost, standing water and debris from areas in which concrete will be placed;
(e) Before fresh concrete is placed against hardened concrete, the contractor shall retighten the forms and clean and moisten the surface of the hardened concrete for bond to the fresh concrete; and
(f) Thoroughly moisten subgrade on which concrete is to be placed. Do not place concrete on frozen subgrade.
(2) Mixing.
(a) All concrete incorporated in the work shall be trans-mixed in accordance with ASTM C94 for ready mix concrete. Small batches of concrete may be job mixed by the contractor when approved by the Engineer.
(b) Addition of water to the concrete during transport or at the site is strictly prohibited.
(c) When placed, the concrete’s temperature shall be between 60°F and 90°F.
(3) Placement.
(a) Convey concrete by methods and equipment capable of supplying concrete from mixer to place of final deposit without segregation and such that detectable setting of concrete does not occur before adjacent concrete is placed.
(b) Use pumping equipment with sufficient deign and pumping capacity to ensure a practically continuous flow of concrete at the point of discharge without segregation. Water shall not be added in order to facilitate pumping.
(c) Limit vertical drop of concrete to four feet unless appropriate equipment is used to prevent segregation.
(d) Do not bear concrete conveying equipment on fresh concrete or reinforcement.
(e) After concrete placing has started, the operation shall be carried on continuously until placement of the section is complete. Do not place a greater section of concrete at one time than can be properly finished.
(f) Deposit concrete as nearly as practicable to its final position to avoid segregation due to rehandling or flowing.
(g) Place concrete at a rate such that the concrete is at all times plastic and flows readily between reinforcement and into corners of forms without segregation.
(h) Do not place concrete that has partially hardened, been retempered or contaminated by foreign materials.
(4) Adverse conditions.
(a) Inclement weather. Do not place concrete during rain, sleet or snow unless adequate protection is provided.
(b) Cold weather.
1. When the air temperature is below 45°F, the contractor shall use special means in mixing and placing concrete to prevent its freezing. If the air temperature is 35°F or less at the time of placing concrete, the water and aggregate shall be heated to a temperature of between 70°F and 150°F by means of steam or heat prior to being placed in the mixes provided uniform results are obtained. When either aggregates or water are heated above 100°F, they shall be combined in the mixes prior to adding cement.
2. Heated enclosures or insulation shall be provided as required to maintain the concrete surface temperature between 55°F and 75°F for a minimum of three days or until the concrete reaches its specified compressive strength.
3. Provide insulation or temporary backfill to protect all earth supported concrete from damage due to frost heaving.
4. Salt, antifreeze solutions or other chemicals shall not be used.
(5) Hot weather.
(a) During hot weather, concrete shall not have a temperature which will cause difficulty from loss of slump, flash set or cold joints. The maximum temperature of concrete during placing shall be 90°F.
(b) Before placing concrete, spray the subgrade, forms and reinforcement with water to keep them cool and to prevent absorption of water from the concrete.
(c) Transport, place and finish concrete as quickly as practicable. Plan concrete delivery, placing techniques and consolidation methods to avoid cold joints.
(d) Start curing the concrete immediately after finishing operations have been completed.
(6) Consolidation.
(a) Thoroughly consolidate all concrete with high frequency vibrators, working the concrete thoroughly around reinforcement and embedded items and into corners of forms.
(b) Use a sufficient number of vibrators, of appropriate size and type, to provide complete vibration throughout the concrete at the same rate it is placed. Provide at least one spare vibrator at the site for use in case of breakdown.
(c) Provide properly spaced vibration of sufficient duration to produce complete consolidation, but not long enough to cause segregation. Continue vibration until mortar begins to puddle at the surface. Remove any excess free water that collects on the surface.
(d) Supplement internal vibration with manual consolidation methods and external form vibration as required to produce concrete free of voids, honeycomb and rough surfaces. Vibrate forms in such a way as to avoid form displacement.
(B) Joints.
(1) Construction joints.
(a) The contractor shall determine, in advance, the location of construction joints and arrange for the quantity of concrete to be poured to locate the joint at the position required by the Engineer. Joints shall be shear keyed as required by the Engineer, and shall be provided with dowel bars, lapping 24 diameters on each side of the joint, corresponding to the reinforcement perpendicular to the joint.
(b) The joint surface of the new concrete previously hardened shall be kept wet for a period of not less than 30 minutes before the placing of new concrete.
(c) Joints shall be perpendicular to the finished concrete surface.
(d) In order to allow for shrinkage, concrete shall not be placed against the second side of the construction joint, including those for columns and walls, for at least 12 hours after placement of the first side.
(2) Expansion joints.
(a) Joints shall be straight and true and cleared of all forming materials and debris. Expansion joint material shall be firmly held in place during placing and finishing of the concrete;
(b) Reinforcement shall not be continued across expansion joints; and
(c) Provide joint filler and sealant materials as specified herein.
(3) Contraction (control) joints.
(a) Construct contraction joints in slabs-on-grade to form panels or patterns indicated on the drawings. Unless otherwise shown, the joint location shall not exceed 30 feet in any direction.
(b) Contraction joints shall be made by saw cutting the concrete. Saw cuts shall be one-eighths-inch wide by one-fourth of the slab depth unless otherwise shown. Cutting shall be sufficient to support the weight of the saw and shall be completed before shrinkage stresses becomes sufficient to produce cracking.
(C) Finishing and curing.
(1) Finishing.
(a) Any defective work discovered after the forms have been removed shall be corrected immediately. All surfaces shall be reasonably free from “honeycombs”, bulging, aggregate pockets and excessive depressions or projections. If any defects cannot be repaired satisfactorily in the opinion of the Engineer, the entire defective section shall be removed and replaced by the contractor at his or her expense.
(b) Immediately after the forms have been removed, all minor depressions resulting from the removal of metal ties, or from other causes, shall be carefully pointed with mortar consisting of one part cement and three parts sand. The surface film of all such filled areas shall be carefully removed before setting occurs.
(c) Sidewalks shall be given a broom finish.
(2) Curing. All exposed surfaces of concrete shall be satisfactorily cured by keeping constantly moist for at least the first five days after placing. If applicable, alternate methods of curing such as a uniform membrane coating, burlap and straw, water-proof blankets or other may be used. New concrete shall not be exposed to the sun or permitted to freeze. Concrete, when poured, shall be protected from rain for at least the six hours following the initial set.
(D) Testing.
(1) Reports. The following information regarding concrete testing shall be provided by written report to the town within three days of completion of the seven-day and 28-day test:
(a) Project identification and portion of structure represented;
(b) Concrete mix class and specified compressive strength requirements;
(c) Weather conditions and air temperature;
(d) Concrete temperature, slump and air content test results;
(e) Dates of placing and testing;
(f) Method of curing (field or laboratory); and
(g) Strength test results.
(2) Strength tests.
(a) During the progress of the work, concrete samples shall be taken for the purpose of taking strength tests in accordance with ASTM C172.
(b) A minimum of four cylinders shall be taken and cured in accordance with ASTM C311 as follows:
1. Each 50 cubic yards of concrete;
2. Each 3,000 square feet of surface area for slabs and walls; and
3. Each class of concrete placed in a day’s work.
(c) Test each group of four cylinders for compressive strength in accordance with ASTM C39 as follows:
1. One field cured cylinder to be tested at seven days;
2. Two laboratory cured cylinders to be tested at 28 days; and
3. One spare.
(d) The compressive strength shall be defined as the average of the strengths of two cylinders made from the same sample of concrete and tested at 28 days.
(e) The compressive strength requirements of an individual class of concrete will be considered satisfactory if both of the following requirements are met:
1. The average of all sets of three consecutive strength tests equal or exceed the specified compressive strength; and
2. No individual strength test (average of two cylinders) falls below the specified compressive strength by more than 500 psi.
(f) If the strength level of an individual class of concrete is found to be unsatisfactory, conduct core testing in accordance with ASTM C42, impactometer testing or load testing on the area of concrete in question as required by the Engineer. If such additional testing does not produce acceptable results, corrective measures will be required to ensure structural adequacy. Make appropriate adjustments to the concrete mix designs as required.
(3) Slump test. A field slump test shall be taken in accordance with ASTM C143 for each group of cylinders required. Concrete batches which do not meet the specified slump ranges shall not be accepted for placement unless otherwise approved by the Engineer.
(4) Air content tests. One air content test shall be taken in accordance with ASTM C173 or ASTM C231 for each group of concrete cylinders which include air entrainment requirements.
(5) Non-conforming concrete. After all testing has been complete, any concrete failing to meet the specified requirements will be rejected and removed and replaced unless otherwise accepted by the town.
(2004 Code, Art. VI, § B, part 3)