Title : SITE MIX CONCRETE
Subject : Procedure for the production and pouring of site mic concrete.
Reference : 1 Project Quality Plan
2 Standard National Indonesia ( SNI)
General.
The work procedure as given herein are to be applied for the production and pouring of site mix concrete. Site mix is intended to be used for the minor elements of the project whwre from the logistic point of view the use of site mix concrete is regarded as more practical. They have to be followed up in line with the guidelines as given in the references above.
Material.
Concrete grade to be used are 2000 PSI for non structural purposes and 3000 PSI for structural purposes. The following material shall be used for site mix concrete, namely:
- Normal Portlan Cement.
- Fine aggreegate ( diameter up to 5 mm). Aggreegat to follow the specification as in the references mentioned above, to be clean from mud or other contamination . Sand to originate from quarry or from natural desegregation or crushing of compact calcareous rock.
- Course aggreegate ( diameter 5 to 20 mm and 20 to 30 mm ) as per specification refered to above . Aggreegate shall be materials from natural sources . Free from shells, mica, gypsum, organic matter or any other impurities.
- Water shall be from the available 6m or deep wells on site and be free from inkourious amounts of oil, acid, alkaline and organic substances.
The pproposed mix design for 2000 PSI and 3000 PSI site mix concrete is as per conditions as set out and determined by the agency responsible for the mixing design. This design mix will be confirmed by a trial mix to be performed under site conditions.
Storage of Material.
Portland cement shall be stored under covered conditions and in such a manner as to provide protection fromm moisture and contamination. Cement shall be stacked in piles not exceeding 13 bag. Long term storage is foreseen in site warehouse as per off ground conditions.
Fine nad coarse aggreegate shall be stored and used in such a way as to avoid excessive segregation and to prevent contamination. The aggreegate will be stored in open conditions but clearly divided by wooden barriers and protected from rain water by plastic sheets as either direct cover or as tarpaulins. Sand shall be allowed to drain until it has uniform moisture content before being used. Water content of teh sand shall be ditermined by meqans of a moisture meter, brand Speedy or equivalent. Water shall be stored in drums clean from oil, acid, alkaline and organic substance. Prior to actual concrete mixing these materials will be transported to teh decentally located concrete mixers on site. Cement will be rationed as per estimated daily requirement of the concrete mixers.
Concrete Mixing.
Mixing concrete shall be performed by portable concrete mixers ( cap. 0,15 m3) located as close as practically possible to the pouring destination. All materials shall be measured by volume with standarad volume containers made from timber based on the proposed mix design. Mixing shall be conducted during a maximum period of 2 minutes , starting from the last material being poured into the mixer, all mixers will be completely emptied bbefore next mixing is to take place.
Concrete Transportation.
From the mixers to the actual pouring site lorries or pails / buckets will be used. These will be emptied with previous concrete and cleansed wiath water before used. In all cases the concrete shall be delivered and discharged within a maximum time limit of 45 minutes.
Concrete Pouring.
Before concrete pouring the surface of the form work shloud be clean and treated with releasing agent with no forign obstacles. Sufficient drainage points have to prepared which need closing before concrete pouring.
Pouring is to be executed in a continous flow working from one point into a specified direction. Concrete shall be placed at such a rate to remain its plasticity at all time during the pour to ensure a readily flowing into the spaces between the rebars. To secure even compaction concrete vibartors should applied continously where practically possibel , the concrete shall be throudhly worked around the reinforcement and existing embedded fixture and into the corners of the forms. Concrete that has partially hardened or has been contaminated by forign matter in the process shall not be used.
Concret e s top s have to be clerly marked and readied by chipping and mortar adding before furthet concreting is to proceed. The concrete stops are only to be prapared when concreting is underbroken or stopped for more than 1.50 hours.
To avoid seggregation the concrete should not be dropped more than 1.50 m high. Horizontal surface finishing of concrete is to be performed through floating immediately after the pouring process. Floating shall begin when the water sheen has disappeared using wooden or steel hand floats. Trueness if surface shall be rechecked with a 2 meter straight edge applied at not less thqn two different angles. High spots shall be cut down and low spots filled upon which refloating is to follow.
Curing of Concrete.
Directly after pouring and up to three days the concrte shlokd be kept damp by spraying water, or alternatively by using matress made from natural fibre such as palm fibre, cotton or staw. Further polythene sheeting can be used to cantain the evaporation of awter during high outside temperatures. The water shall be from the 6 m or deep well available on site and be free injurious amonts of oil, acid, salt, alkaline and organic substances.
Sampling and Testing.
Sampling shall be done to inspect on the actual concrete quality on site. Each concrete pouring day 2 slump tests shall be performed on site according ti the Indonesian standard on slump test. The result shall be compared with the allowable slump as given in the construction specification.
For commpression test based on cylinder testing as per 30 cm x 15 cm standard volume, each concrete pouring day 1 sample shall be taken in teh morning followed by 1 more sample in the afternoon. These samples shall be tested on 7 days ( three cylinders ) and 28 days ( three cylinders ) on compressive stength as specified in the construction specs. Prior ti testing the samples shall be cured underwater in a proper place, either Contractor's warehouse or the inspection agency's storage area.