Before permitting any concrete to be placed, you must submit a "hard card" to the ROICC or the OPS Department. A "hard card," or Concrete Placement Clearance Form (fig. 6-7), is a checklist to be completed before placement of the concrete. This is an excellent checklist for you to ensure yourself and the ROICC that every aspect has been thoroughly covered and your crew is ready to place the concrete.
You must make sure that the formwork complies in all respects with the applicable requirements of the specifications. When old forms are reused, make sure they have been properly repaired and cleaned. If the forms are of considerable height, you must see that openings have been provided as necessary for placing concrete without excessive drop. See chapter 4 for these requirements. Before placing concrete, you must make sure that all debris has been completely removed from inside the forms and that the contact surfaces of the forms have been wetted, oiled, or coated as specified. Generally, form contact surfaces are oiled before being erected. When used for footings, abutments, and other large sections, you should oil the forms after erection if care is taken to avoid getting oil on the reinforcement.
All reinforcement must be checked in detail to make sure that it is of the specified size, length, type, form, and spacing; is clean and free from loose rust or scale; is firmly secured by approved devices against displacement; and is accurately located to assure that the required cover will be obtained. Splices must be checked for location, length of lap, clearances between bars, and clearance of bars to forms and dirt. When welded butt or lap splices are required or permitted, you must check the quality, the size, and the amount of weld.
You must be sure that all anchors, inserts, dowels, sleeves, pipes, and similar fixtures that have to be embedded in the concrete are accurately placed and firmly secured to the forms. Before and during placing operations, you must check the concrete mixture for conformity with specifications. This means verifying slump tests, air-entrainment tests, and the preparation of laboratory test samples for compressive and flexural strength tests.
When ready-mixed concrete is to be used, you must ensure the requirements of the specifications for the method of mixing and delivery are fully met. When job mixing at a central plant at the site is adopted, make sure the methods of transporting the concrete assure rapid delivery without segregation or loss of material.
Concrete may be conveyed from the mixer or delivery point to the forms by carts, buckets, chutes, pneumatic methods, pumping, or tremie.
You must make sure that the methods and equipment meet with the approval of your superior when so required. You must, in all cases, be satisfied that the concrete, as placed, is acceptable in all respects and likewise require correction of deficiencies in methods or equipment if the concrete is not of acceptable quality. You must make sure that the concrete does not displace the reinforcement and that construction joints and expansion joints are provided at all required locations and are properly located and formed. If concrete is placed in cold weather by a tremie or under other special circumstances, you must make sure that the special precautions required are taken.
You must remember the importance of uniformity of the finish and the surface texture. To inspect, you should familiarize yourself with the proper techniques for achieving satisfactory results and with the causes and methods of avoiding the common defects in the finish. Excessive surface water, for example, results from too wet or too sandy a mix or from overworking. Such excess water should be removed by blotting methods or by evaporation, and not by sprinkling dry cement on the surface. Excessive troweling brings laitance to the surface and gives a surface that soon dusts and deteriorates. The drying of concrete too rapidly leads to hair cracks. Placing a topping over dry concrete causes alligator cracking from rapid absorption of water by the base course. You must assure yourself that the methods and techniques used prevent such defects and deficiencies.
Specifications contain specific requirements for the protection and curing of concrete, including special requirements for certain cases. You must determine which requirements are correct for the project. You should give careful attention to the requirements for the length of the curing period required and the length of time forms or supports must be kept in place. You must make sure that the curing methods fully protect the concrete against drying out prematurely. If membrane water proofing is permitted, make sure that the membrane seal is applied so that no gaps or holidaysContinue Reading