9.1 Quality Assurance Measures
9.1.1 In order that the properties of the completed structure be consistent with the requirements and the assumptions made during the planning and the design, adequate quality assurance measures shall be taken. The construction should result in satisfactory strength, serviceability and long term durability so as to lower the overall life-cycle cost. Quality assurance in construction activity relates to proper design, use of adequate materials and components to be supplied by the producers, proper workmanship in the execution of works by the contractor and ultimately proper care during the use of structure including timely maintenance and repair by the owner. The maintenance plays an important role in sustained durability of concrete.
9.1.2 Quality assurance measures are both technical and organizational. Some common cases should be specified in a general Quality Assurance Plan which shall identify the key elements necessary to provide fitness of the structure and the means by which they are to be provided and measured with the overall purpose to provide confidence that the realized project will work satisfactorily in service fulfilling intended needs. The job of quality control and quality assurance would involve quality audit of both the inputs as well as the outputs. Inputs are in the form of materials for concrete; workmanship in all stages of batching, mixing, transportation, placing, compaction and curing;
| Table 9 Proportions for Nominal Mix Concrete(Clauses 8.3 and 8.3.1) | ||||
| Sl No. | Grade of Concrete | Total Quantity of Dry Aggregates by Mass per 50 kg of Cement, to be Taken as the Sum of the Individual Masses of Fine and Coarse Aggregates kgMax | Proportion of Fine Aggregate to Coarse Aggregate (by Mass) | Quantity of Water per 50 kg of Cement1 |
| (1) | (2) | (3) | (4) | (5) |
| i) | M 5 | 800 | Generally 1:2 | 60 |
| ii) | M 7.5 | 625 | but subject to an upper limit | 45 |
| iii) | M 10 | 480 | 34 | |
| iv) | M 15 | 330 | of and a lower limit of | |
1 The proportion of the fine to coarse aggregates should be adjusted from upper limit to lower limit progressively as the grading of fine aggregates becomes finer and the maximum size of coarse aggregate becomes larger. Graded coarse aggregate shall be used.
Example
For an average grading of fine aggregate {that is, Zone II of Table 4 of the accepted standard [6-5A(12)]}, the proportions shall be , 1:2 and for maximum size of aggregates , and , respectively.
2 Quantity of water required from durability point of view may be less than the value given above.
and the related plant, machinery and equipment; resulting in the output in the form of concrete in place. To ensure proper performance, it is necessary that each step in concreting which will be covered by the next step is inspected as the work proceeds (see also 16).
9.1.3 Each party involved in the realization of a project should establish and implement a Quality Assurance Plan, for its participation in the project. Supplier's and subcontractor's activities shall be covered in the plan. The individual Quality Assurance Plans shall fit into the general Quality Assurance Plan. A Quality Assurance Plan shall define the tasks and responsibilities of all persons involved, adequate control and checking procedures, and the organization and maintaining adequate documentation of the building process and its results. Such documentation should generally include,
a) test reports and manufacturer's certificate for materials, concrete mix design details;
b) pour cards for site organization and clearance for concrete placement;
c) record of site inspection of workmanship, field tests;
d) non-conformance reports, change orders;
e) quality control charts; and
f) statistical analysis.
PART 6 STRUCTURAL DESIGN — SECTION 5 CONCRETE: 5A PLAIN AND REINFORCED CONCRETE
NOTE — Quality control charts are recommended, wherever the concrete is in continuous production over considerable period.
9.2 Batching
To avoid confusion and error in batching, consideration should be given to using the smallest practical number of different concrete mixes on any site or in any one plant. In batching concrete, the quantity of both cement and aggregate shall be determined by mass; admixture, if solid, by mass; liquid admixture may however be measured in volume or mass; water shall be weighed or measured by volume in a calibrated tank {see also accepted standard [6-5A(23)]}.
For large and medium project sites, the concrete shall be sourced from ready-mixed concrete plants or from captive on-site or off-site automatic batching and mixing plants. The concrete produced and supplied by ready-mixed concrete plants shall be in accordance with good practices [6-5A(24)]. In case of concrete from captive on-site or off-site automatic batching and mixing plants, similar quality control shall be followed.
9.2.1 The grading of aggregate shall be controlled by obtaining the coarse aggregate in different sizes and blending them in right proportions, the different sizes being stocked in separate stock-piles. The material should be stock-piled for several hours preferably a day before use. The grading of coarse and fine aggregate should be checked as frequently as possible, the frequency for a given job being determined by the Engineer-in-Charge to ensure that the specified grading is maintained.
9.2.2 The accuracy of the measuring equipment shall be within percent of the quantity of cement and mineral admixtures being measured and within percent of the quantity of aggregate, chemical admixtures and water being measured. In a batching plant, the concrete production equipment shall be calibrated initially at the time of installation or reconditioning of the equipment and subsequently at the following intervals:
a) Mechanical/knife edge: At least once every systems two months
b) Electrical/load cell systems : At least once every three months
9.2.3 All ingredients of concrete shall be used by mass only except water and chemical admixtures, which may be by volume.
9.2.4 Volume batching may be allowed only where weigh-batching is not practical and provided accurate bulk densities of materials to be actually used in concrete have earlier been established. Allowance for bulking shall be made in accordance with accepted standard [6-5A(25)]. The mass volume relationship should be checked as frequently as necessary, the frequency for the given job being determined by Engineer-in-Charge
9.3 Mixing
Concrete shall be mixed in a mechanical mixer {(see also the accepted standard [6-5A(26)]}. It shall be ensured that stationary or central mixers and truck mixers shall comply with the performance criteria of mixing efficiency as per the accepted standard [6-5A(27)]. Mixing efficiency test shall be performed at least once in a year. The mixers shall be fitted with water measuring (metering) devices. The mixing shall be continued until there is a uniform distribution of the materials and the mass is uniform in colour and consistency. If there is segregation after unloading from the mixer, the concrete should be remixed.
9.3.1 As a guidance, the mixing time shall be at least 2 min for conventional free fall (drum) batch type concrete mixers. For other types of more efficient mixers, manufacturer's recommendations shall be followed.
9.3.2 Workability should be checked at frequent intervals {see accepted standard [6-5A(20)]}.
9.3.3 Dosages of retarders, plasticizers and superplasticizers shall be restricted to 0.5, 1.0 and 2.0 percent, respectively by mass of cementitious materials; however, the dosages of polycarboxylate based admixtures shall not exceed 1.0 percent. A higher value of above admixtures may be used, if agreed upon between the manufacturer and the constructor based on performance tests relating to workability, setting time and early age strength.