Cement w2b5c

Cement Cement is a hydraulic binder. That is a finely ground inorganic material which, when mixed with water, forms a paste which sets and hardens by means of hydration reactions. Also after hardening it retains its strength and stability even under water.

Tokyo Cement Company is one of the leading cement manufacturing companies in Sri Lanka. They manufacture various types of cement under different brand names. Cement types 1 Ordinary Portland cement (OPC) 2. Portland Pozzolana Cement (PPC) 3. Masonry Cement Other products are Tokyo super bond and Tokyo super mix (pre mix) concretes. Concrete Concrete is a mixture of cement, water, sand and metal Ready mix concrete Tokyo ready mix is the pioneers of the ready mix concretes in Sri Lanka. Our ready mix plants are situated at Peliyagoda, Trincomalee, Kandy, Jaffna, Elpitiya, Aluthgama and Anuradhapura. Raw materials of concrete Concrete consists of the contribution of several raw materials such as: 1. 2. 3. 4.

Cement Sand (fine aggregate) Metal (coarse aggregate) ixtures

We should test each raw material before batched and the following tests should be done on raw-materials.

Cement Usually, we measure the water consistency, initial and final setting time of cement for every shipment. Instrument- vicat apparatus I have done this test according to SLS standard and the following table shows the test results of the test. Sample reference TCCT 27

Water consistency 27.25%

I. setting time 130 min

F. setting time 205 min

According to standard specification, the initial setting time should not less than 60 minutes and the final setting time should not exceed 10 hours. Furthermore, we should test the compressive strength of the test cube using those cement samples. Age of cube to be test – 3 day 7 day 28 day If need we test 1 day strength also

Sand We purchase sand from several suppliers. Therefore, each truck should be visually tested before accepted and the accepted samples are stored in a specific area in the plant. Other test for sand are – bulk density Specific gravity Sieve analysis Clay, silt and dust Water absorption Moisture content Metal We purchase metal from several suppliers .Therefore, each truck should be visually tested before accepted and the accepted samples are stored in a specific area in the plant. Other test for metal are – bulk density Specific gravity Sieve analysis

Water absorption Flakiness index We should check the shape of metal when purchasing because it affects the workability and durability of concrete. Shapes of coarse aggregates are divided into five categories as rounded, irregular, angular, elongated and flaky. ixtures ixtures are chemical substances that enhance the workability and durability of concrete. There are several types of ixtures and manufactures. The brand name, which we use, is Grace. The types of grace ixtures, that we use, are Daratard 17 (D 17) Chemical nature - hydroxylated organic compound Mode of action - retards the initial and final setting time and also D-17 reduce the water 7-10% in a concrete mixture Daracem 100 (D 100) Chemical nature – naphthalene sulphonates and modified lignosulphonates Mode of action - retardation of setting time and improved slump retention Adva 181 Chemical nature - polymer compound Mode of action –

Bara emulsion 57 D (BE57D) Chemical nature - styrene butadiene copolymer Mode of action - It acts as water proofing agent and strong bonding agent. Site visits I have participated in several site visits such as china geo (modara), china geo (gothatuwa), and rhino roofing (ekala). I observed and learned some technical activities at those site visits. They are,

1. Slump test 2. Cube casting 3. Rebound hammer test Slump test Slump test is the most commonly used method of measuring consistency of concrete. It can be employed either in laboratory or at site. Apparatus -slump cone (metallic mould) Height- 300 mm Top diameter 100 mm Bottom diameter 200 mm Cube casting Normally we should test the compressive strength of each product customer wisely. Therefore, we measure and record the compressive strength of each cube. Compressive strength of concrete is classified as 3 day, 7 day and 28 day strength.

Rebound Hammer test When compressive strength of test cubes fails, we have to go for a rebound hammer test at client’s request. Finally, we should issue the test report to the construction company, which made the request. Rebound hemmer test (procedure) *Firstly, the affected area is observed. *Then mark several points in the selected area *Draw the square and it is divided into 16 sub squares as follows

1 5 12 13

2 6 11 14

3 7 10 15

4 8 9 16

*then take the rebound hammer reading from each squares *finally, we give the reading as average

Crack repairing Normally cracks in concretes occur due to various factors such as temperature, improper placing, improper compacting and improper curing. If any concrete cracks, we have to repair it. In this situation, we use Bara emulsion to repair the cracks on the concrete. The Bara emulsion acts as a bonding and water proofing agent. I have already participated in crack repairing.

Process of manufacturing concrete Main steps of manufacturing concrete are 1. Batching – measurement of materials for concrete 2. Mixing – mixing is essential for the production of uniform concrete 3. Transporting –concrete can be transported by variety of methods (Ex-truck mixer, mortar pan, pump and pump line etc.) 4. Placing - for good enough concrete must be placed in systematic manner 5. Compacting 6. Curing 7. finishing

Plant operation Following picture shows the sketch of entire plant area. There are two cement silos named S-01 and S-02, which include ordinary Portland cement and Portland pozzolana cement respectively. Ordinary Portland cement is used for any kind of concrete whereas pozzolana cement is used for special cases only such as if site is situated at marshy land area or highly sulphur affected area.

In addition to other units there is very special unit, which is known as chill water unit. Its function is to produce ice water. As per the clients’ request, we have to maintain temperature of the concrete and under this condition we use chill water for making concrete. According to the mix design, the plant operator selects the relevant ratios of raw materials. and after, automatically, mixing, the concrete paste is unloaded into the truck. 

We should always maintain stockpiles of raw materials under the Surface Saturated Dry condition.  We should size separate of fine aggregate using sieve before enter the mixing unit  We should test suitability of water for concrete once a year under British Standard 812 or Sri Lanka Standard 522.  And also other raw materials should be within the acceptable range for making concrete. End of the day we should clean the mixing unit properly. Mix design There are several requirements for making new concrete design. They are: *characteristic compressive strength *type of cement *workability *maximum aggregate size *maximum free water /cement ratio *maximum cement content *minimum cement content *exposure condition *nominal cover to reinforcements Proportions of materials such as cement, water, aggregates and ixtures are changed according to the above mentioned requirements. Always, we try to reduce the water/cement ratio of mix design which affects on the strength of the concrete. If we add more water than required water content capillary voids of concrete is raised. The capillary voids reduce the strength of concrete. Therefore, we should minimize the capillary voids in concrete by controlling the water content. The special mix designs have been developed to overcome that case.

At this time I have started to study and do ISO documentation process. I have done the following test under the British standards for ISO document and laboratory quality control process.