Mass_Concrete Method Statement

QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

Mass Concrete & Controlling Temperatures in the Mass Concrete By ITD Concrete Batching Plant

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

Table of Contents 1.) Purposes 2.) Scope of Works 3.) Controlling Temperatures in the Mass Concrete 3.1 ) Concrete Mixing & Supply 3.2) Concrete Placement 3.3) Curing Procedure 4.) Illustration Picture from Other Similar Projects Appendix : Technical Public & Research Reference

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

1.) PURPOSES Temperature control of mass concrete1 is necessary to prevent cracking caused by excessive tensile stains that result from temperature differential within the concrete mass. Cracking can be controlled by methods that limit the peak temperature to a safe level. This method statement has been prepared to provide a general guide, special considerations to be given in relation to the heat of hydration for concrete pours. This method statement describes the work procedures to be carried out during an execution stage of Pelletizer Structure foundations at gridlines 51A/511,51A/512,51A/513,51B/511,51B/512 and 51B/513 respectively, of which the character of the concrete is technically specified as a mass concrete foundations viz. they are concrete structures with large dimensions simply figured of greater than 1.50 meters for all dimensions. The entire procedure can be organized into 3 steps. First step is a pre-cooling procedure with will be applied at the concrete batching plant to achieve a minimum concrete temperature supply. Second step is to minimize time delivery of concrete since being dispatched from batching plant to the workface and to minimize time spending before concrete placement at the workface and third step is a post-cooling procedure with will be applied during concrete curing upon a completion of concrete placement. A temperature differential between the center of the concrete mass and any about the outside faces will be kept minimum ( Basically , heat on the surface of the concrete is easily released toward the ambient whereas the center remains its high temperatures , this follows that the temperature differential will induce the internal restraint and subsequently introduce thermal contraction cracks. The method statement also includes details of temperature differential control procedure during concrete placement with related to pouring sequence. Special care and planning is required as the volume of pour is large in relation to those normally being place on the workface.

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ACI 116R : Cement and Concrete Terminology concrete, mass—any volume of concrete with dimensions large enough to require that measures be taken to cope with generation of heat from hydration of the cement and attendant volume change, to minimize cracking. ACI 207 ,4R-93 : Cooling and Insulation System for Mass Concrete—2.3-Structure dimensions Where the least dimension of a concrete unit is not large, the concrete mixture is low in heat evolution, and the heat of hydration can escape readily from the two boundary surfaces (forms not insulated), the maximum temperature rise will not be great. Note : Because the definition does not provide a specific measure, many agencies have developed their own definitions of mass concrete.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

2.) SCOPE OF WORK This method statement includes e.g. pre-cooling procedure before & during concrete mix, supply & delivery of concrete, inspection of concrete at the workface and postcooling by a proper cooling upon a completion of concrete placement.

3.) CONTROLLING TEMPERATURES IN THE MASS CONCRETE 3.1) Concrete Mixing & Supply: With a large concrete pour of this magnitude it is

essential that proper pre-construction planning methods and proper checks be in place prior to execution of the works. A mass pour is considered to be demanded a special attention to be given to logistical and technical considerations such as concrete supply, casting sequence and temperature differential control by thermal quilts curing method etc. Finally, a report of temperature monitoring will be conducted. • Concrete Mix Control (Pre-Cooling Procedure): It is a preparation against the possible effect to the concrete properties and construction operations. When these factors are explained to the relevant persons engaged to these activities therefore measures will be taken to eliminate or minimize undesirable effects that possibly introduced. This method defines lists of possible unfavorable effects and prevents practices intended to minimize them. Among these practices are such important measures as a pre-cooling ingredient, consideration of concrete temperature as placed, transportation time and curing technique. The method of concrete temperature control will be proposed as follows: (a) Use of ice as part of mixing water2: This application is effective in reducing concrete temperature, because on melting alone, to absorb heat. The following measures will be applied: ¾ Spray cool water continually approximately at every 30 minutes interval to the course aggregate stock3. This will be done at least 2 hours in advance prior to mixing of concrete.

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ACI 207 ,4R-93 : Cooling and Insulation System for Mass Concrete— 3.3.2 Using ice as batch water -One lb (kg) of ice absorbs 144 Btu’s (334 kJ) when it changes from ice to water; thus, the use of ice is one of the basic and most efficient methods to lower concrete placing temperatures. The earliest method involved the use of block ice that was crushed or chipped immediately before it was batched. Later methods utilized either ice flaking equipment, where ice is formed on and scraped from a refrigerated drum that revolves through a source of water; or equipment where ice is formed and extruded from refrigerated tubes and is clipped into small biscuit-shaped pieces as it is extruded.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

¾ Add ice as a part of mixing water for the concrete mix to reduce the water temperature. The ice will be added until the water temperature is reduced to reach 8-10 Celsius Degree. The amount of ice added to the water is dependent on the air temperature at the certain mixing day. ¾ Spray cool water to the trucks mixers to reduce the temperature of the trucks mixers. ¾ At the batching, the first batch of the concrete shall be checked its temperature. The water temperature will be continued to reduce until the concrete temperature is lower than 30 Celsius Degree prior to the delivering to the workface. ¾ The above process will be regularly done during the entire period of supply to ensure that the same degree of temperature always be maintained. ¾ At the workface upon a delivery of the concrete, the fresh concrete will be remeasured whether the temperature is still within the specified tolerance. (b). Using Low Heat Concrete: mix design for low heat concrete mix will be submitted for approval prior to use. In addition, trail mix will be done prior to use.

Concrete Delivery4 : since the temperature rise can be increased with a passage of time thus the period between mixing and delivery will be kept to an absolute minimum. Attention will be given to coordinating and dispatching of the mixing trucks with the rate of placement to avoid delays in delivery. Details are as follows: Planning: A pre-concreting meeting will be held internally and with concrete supplier to finalize agreement of the proposed concreting procedure. Access: Designated site access routes for concrete supply will be prepared and traffic control measures implemented. The proper access must be organized to enable a continuous transportation of the concrete during the entire period of pouring so that the required temperature of concrete pour will be maintained. Supply: Concrete batching plant capacity and numbers of delivery trucks will be planned to maintain a continuous supply of concrete so that an introducing to 3

ACI 207 ,4R-93 : Cooling and Insulation System for Mass Concrete— 3.4- Aggregate cooling Although most rock minerals have a comparatively low unit heat capacity, aggregates comprise the greatest proportion of concrete mixtures. Therefore, the temperature of the aggregates has the greatest influence on the temperature of the concrete. Under the most severe temperature conditions of construction, the objectives of a comprehensive temperature control program cannot be achieved without some cooling of the concrete aggregates. 3.4.3 Sprinkling of coarse aggregate stockpiles-Misting or sprinkling water onto coarse aggregate stockpiles is an inexpensive but limited means of reducing coarse aggregate temperatures. The amount of cooling that can be obtained depends upon the cooling effect of natural evaporation, which in turn, depends upon the ambient conditions of temperature, wind, and relative humidity.

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ACI 305R-99 Hot Weather Concreting—3.4—Delivery : Cement hydration, temperature rise, slump loss, aggregate grinding, and either loss or, occasionally, gain of air content all occur with the passage of time while the concrete is in the mixer; thus, the period between start of mixing to start of placement of the concrete should be minimized. Coordinating the dispatching of mixer trucks with the rate of concrete placement avoids delays in arrival or waiting periods until discharge. On major concrete placements, provisions should be made to have good communications between the job site and concrete-production facility. Major placements should be scheduled during periods of lower urban traffic loads. When placement is slow, consideration should be given to reducing load size, using set-retarding admixture, or using cooled concrete.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

cold joint can be prevented. In addition to minimize temperature differentials occurred within the concrete mass during pour. Pouring: Concrete will be placed in a predetermined sequence to avoid any possibility of an excessive temperature differential and cold joint formation within the foundation. Quality Control: Sufficient quality control measures will be set up in place for checking concrete supply and deliveries throughout the duration of the pour.

3.2) Concrete Placement: Due to one-go casting of each raft foundations /structures

the concrete pouring should be executed during the night time in order that the workface temperature can be minimized during the entire placement period.

Sufficient concrete pumps will be engaged for concrete placement in order that a flow pouring can be achieved. As such parking time of the concrete trucks waiting for pouring can be kept minimized thus the required placing temperature will be maintained.

3.3) Curing Procedure:

The set of foams and plastic sheets will be used for curing purposes. This will be done immediately once the concrete is reached its stiffening time by fully cover the whole concrete surface and spread the sand (approximately 10 mm. thick.) onto the whole area of plastic sheets to prevent concrete temperature loss too quick and result high temperature differential between the surface and at the middle. Care must be taken during the entire curing to ensure by reading its temperature through a set of thermocouples that the temperature at the middle of the concrete and any outer surface to be kept minimum.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

3.4) Test and Monitoring of the Concrete Mass after Poured As soon as the concrete has reached its stiffening time approximately 1 hour after pouring a set of plastic sheet will be covered fully the concrete surface. Sand will be filled fully onto the whole area where the plastics sheet cover with approximately 10mm. thick. The plastics cover and the side forms will be maintained to ensure that the temperature differential between the middle of concrete mass and any outer surface can be kept minimized

(1) Thermocouple Installation

(2) Digital Thermometer

To ensure that the temperature differential will be controlled a set of measuring apparatus will be set as shown by the above pictures. The measurement purposes are to finding the temperature development within the concrete mass. The results will show peak temperature and the temperature differential for such measuring points. As previously explained, sets of thermocouples will be installed and embedded to the concrete at the bottom, middle and. Top and bottom sets will be approximately 30 cm of measuring from the edges. The heat generated will be converted to the circuit and sent to the digital thermometer which will record and show information of temperature measure. In general case the maximum temperature of mass concrete will peak at 48 hours after pour and will be constant for 7 days and will decrease to the air temperature after 14 days

Equipment Installation: Temperatures will be measured at 3 levels e.g. top, middle and bottom. The end of each thermocouple wire(s) were fixed to the designated position to the concrete mass prior to pouring. The others ends were linked to the rear panel of the digital thermometer which is set to read the temperature at every 60 minutes for at least 3 day.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

4. ILLUSTRATION PICTURES FROM OTHER SIMILAR PROJECTS As previously described the temporary control have been controlled in various possible means as illustrated below. Control Concrete Mix at the Batching Plant At the concrete batching plant approximately 3-4 hours in advance pre-cooling of the mixing components were done as follows. ¾ Temperature Control of Water before Concrete Mixing

Fig (1) Pre-Cooling Water Tank Figs (1) At the earliest stage of water pre-cooling the cube ice were filled to the water tanks. Thus to be the most effectiveness just 1-2 hours prior to concrete mixing the crushed ice has been placed directly into the water tanks as part of mixing water. The crushed ice was maintained adding to the water for the entire concrete placing.

Pre-Cooling water to the water tanks for 3-4 hours in advance has been done prior to concrete mixing in order to effect a moderate reduction in concrete placing. Pre-Cooling in water temperatures were accomplished by mechanical refrigeration, using ice as part of mixing water. Because on melting alone it absorbs heat at the high rate, just 1-2 hours prior to concrete mixing thus to be the most effective the crushed ice were placed directly into the mixing water in the tanks. The ice will be added until 8-10 Celsius Degree of water temperature is reached and to maintain until the total volume of concrete is poured.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

¾ Pre-Cooling Coarse Aggregate

Fig (2) Fig (2) At the batching plant, approximately 2-3 hours in advance prior to concrete mixing, the aggregate were sprayed continually at every 30 minutes interval with water to minimize its temperature.

¾ Pre-Cooling Cement in the Silo

Fig (3) Fig (3) Cement in the silos being pre-cooled with water sprayed at every 30 minutes interval. This was done at approximately 2 hour in advance prior to concrete mixing

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

¾ Control Concrete Temperature prior to Concrete Placing

4 (a)

4 (c)

4 (b)

4 (d)

Fig (4) Fig 4: A set of thermocouple were installed at the selected locations.4 (a) The thermocouples were installed at the nominated exterior points. 4(b) The thermocouples were installed at the nominated interior points.4(c), 4(d) All the concrete trucks prior to pouring at the workface were parked at the QC Inspection Station to test and keep records for their slumps and temperatures. The allowable slump is between 7.5-12.5 cm. and the allowable arrival temperatures are not beyond 30 degree Celsius.

¾ Control Concrete Temperature after Placement (Post-Cooling)

Fig (5) Fig (5): On a completion of concrete placement, as soon as the concrete reached a stiffening point, the entire surface area of concrete was immediately covered with 2 inch thick foams, plastic sheet and 10 cm. thick layer of sand for the 1st, 2nd and 3rd layer respectively. The side form was left un-dismantling for 2 weeks. The temperatures were recorded for every 1 hour at the first 48 hours after concrete placement and at every 2 hours for the rest.

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QA/QC Section Mass Concrete & Controlling Temperatures in the Mass Concrete

APPENDIX: TECHNICAL PUBLIC & RESEARCH REFERENCES

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