K1-Report

ABSTRACT

The objective of this experiment is to determine the standard consistency and initial setting time of cement paste. There are two types of cement mixture samples used in this experiment. They are Ordinary Portland Cement (OPC) and composite cement which is the combination of 99.5% of OPC and 0.5% of calcium carbonate (CaCO 3). After the experiment, experiment, the results of the two types of cement mixture samples are compared. Initially, we determined the water required for a specified weight of cement to achieve the requirement of standard consistence. The specified weight of cement used in this experiment was 500 gram. The consistency of the cement was tested and examined by using the Vicat apparatus. In our first trial, we assumed 152 ml and 161 ml of distilled water required for OPC and the composite cement respectively. The test was repeated by altering the volume of water content added to the cement mixture until the plunger penetration readings remained remained at (6 ±2) mm. In our experiment, we succeeded in our second trial by using 156ml of distilled water for OPC cement mixture and 158ml of distilled water for composite cement mixture, resulting in 8mm and 7mm of plunger penetrations respectively. After the amount of water required for the cement mixture was identified, the experiment was proceeded to determining the initial setting time for both two types of cement mixtures. The early setting time for cement mixtures were determined by using (1.13±0.05) mm needle installed in the Vicat apparatus. The moulds containing the cement mixture prepared will be submerged in a container of water at temperature of (20±2) ºC based on the BS EN 196-3:2005. The purpose of this step is to speed up the hydration  process of cement mixture. mixture. The length of needle penetrated penetrated into both cement samples will be recorded recorded in the interval of 10 minutes until it fulfilled the requirement of (6 ±3) mm penetration. The initial setting time for OPC is 130 minutes and the composite cement set slightly earlier which was 120 minutes. Both cement mixtures achieved 6mm needle penetration at the time mentioned earlier. In short, composite cement with the addition of 0.5% of calcium carbonate has higher water demand but took shorter time to set as compared to OPC cement.

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OBJECTIVE

To determine the standard consistency and initial setting time of Ordinary Portland Cement (OPC) and composite cement (99.5% of OPC with 0.5% of calcium carbonate).

INTRODUCTION

Ordinary Portland Cement (OPC) and composite cement are used to determine their standard consistency and initial setting time. The standard consistency and initial setting time for OPC and composite cement are different as they are affected by cement fineness, chemical content and the present of admixtures which are different in both OPC and composite cement. In an operation on project site, determination of standard consistency is important to ensure the cement mixture produced are workable and it is very important in the process of placing and compaction of operation. The concrete mixture is tested through standard consistency test by using Vicat apparatus in which the suitable water content added into cement mix is determined. The standard consistency of cement paste is defined as their consistency that will permit the Vicat plunger to penetrate the cement paste until the end of the plunger and the base of cement paste is at distance of (6±2) mm. Also, we should know the initial setting time of cement mixture for the purpose of transportation of cement mixture to project site. The initial setting time of concrete is the time interval between the mixing of cement with water and the time when the mix has lost its plasticity to a certain stage. The initial setting time of cement mixture is determined by Vicat apparatus with needle. The cement mixture is said to be set when the needle of Vicat apparatus penetrate the paste until it ends (6±3) mm from the base of  plate.

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EQUIPMENT AND MATERIALS

a) For General Usage : i.

Weight balance

ii.

Measuring cylinder

iii.

Distilled water

iv.

Stopwatch

v.

Bowl

vi.

Ordinary Portland Cement

vii.

Calcium Carbonate (CaCO 3)

 b) For Standard Consistence Test : i.

Vicat apparatus

ii.

Vicat mould

iii.

Plunger with 45mm in length and (10.00±0.05) mm in diameter

iv.

Base-plate constructed of impermeable material

c) For Initial Setting Time Test : i.

Container

ii.

Temperature controlled enclosure

iii.

Vicat apparatus

iv.

Vicat needle of (1.13±0.05) mm in diameter

v. vi.

Vicat mould Base-plate constructed of impermeable material

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PROCEDURE a) Mixing the cement paste

Ordinary Portland Cement (OPC) with the weight of 500g in the accuracy of ±1g and an amount of distilled water (e.g. 125ml) are prepared. When distilled water is measured by volume using graduated cylinder or burette, it shall be dispensed to an accuracy of ±1ml. Both cement and distilled water are place into a bowl with full attention to avoid loss of water or cement. The addition should  be completed within 10s. The cement mixture is then mixed manually in a constant speed for 3 minutes. The cement mixture is then transferred immediately to the lightly oiled mould which has  previously been placed on the lightly oiled base-plate to excess without under compaction or vibration. Any voids in the paste are removed by gently tapping the slightly overfilled mould against the ball at the hand. The excess is removed by a gentle sawing motion with a straight-edged implement in such a way as to leave the paste filling the mould and having a smooth upper surface. The test is repeated by replacing OPC cement with composite cement which consists of 99.5% of OPC and 0.5% of calcium carbonate. b) Standard Consistency Test

The Vicat apparatus is adjusted with the plunger attached to it in advance of the test. The  plunger is lowered to rest on the base-plate to be used and the pointer or the scale is adjusted to zero reading. Then, the plunger is raised to the stand-by position. Immediately after levelling the paste, the mould is transferred to the Vicat apparatus and positioned centrally under the plunger. The plunger is lowered gently until it is in contact with the paste. The position is paused for between 1s to 2s. The  plunger is then released quickly to allow the plunger to penetrate vertically into the centre of the  paste. Plunger released shall occurred in 4 min ± 10 s after zero time. The scale is read at least 5s after  penetration has ceased or 30s after the plunger is released, whichever is the earlier. Next, the scale reading is recorded, which indicates the distance between the bottom face of the plunger and the base plate, together with the water content of the paste expressed as a percentage by mass of the cement. The plunger is cleaned immediately after each penetration. The test is repeated with pastes containing different water contents until one was found to produce a distance between plunger and base-plate of (6 ± 2) mm. The water content of that cement paste is recorded to the nearest 0.5% as the water for standard consistence. The test is repeated by replacing OPC cement with composite cement which consists of 99.5% of OPC and 0.5% of calcium carbonate.

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c) Determination of Initial Setting Time

A Vicat mould is filled in the accordance with paste of standard consistence mixed in accordance with volume of water content and weight of cement. The filled mould and base-plate are  placed in the container, water is added so that the surface of the paste is submerged to a depth of at least 5mm, and stored in the temperature controlled enclosure at 20 ºC (±1.0 ºC). After 10 minutes, the mould base plate and container are placed under the needles of the Vicat apparatus. The needle is lowered gently until it is in contact with the paste. That position is paused in for between 1s and 2s in order to avoid initial velocity or forced acceleration of the moving parts. Then the moving parts are released quickly and the needle is allowed to penetrate vertically into the paste. The scale is read when the penetration has ceased, or 30s after the release of the needle whichever is the earlier. The scale reading is recorded, which indicates the distances between the end of the needles and the base  plate, together with the time from zero. The penetration is repeated on the same specimen at conveniently spaced position, and not less than 8mm from the rim of the mould or 5mm from each other and at least 10mm from the last penetration. Between penetrations, keep the specimen in the container in the temperature controlled enclosure. The Vicat needle is cleaned immediately after each  penetration. The time measured from zero to the time at which the distance between the needles and the base-plate being (6±3) mm is recorded as the initial setting time of the cement to the nearest 5 minutes. The test is repeated by replacing OPC cement with composite cement which consists of 99.5% of OPC and 0.5% of calcium carbonate.

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RESULTS a) Standard Consistency Test

OPC Volume of distilled

Value of Penetration / Vicat

water (ml)

Reading (mm)

First

152

9

30.5

Second

156

8

31.0

Trial

Water Content (%)

OPC and 0.5% of CaCO 3 Volume of distilled

Value of Penetration / Vicat

water (ml)

Reading (mm)

First

161

3

32.0

Second

158

7

31.5

Trial

Water Content (%)

b) Initial Setting Time Test

Time (minute)

Value of Penetration / Vicat Reading (mm) OPC

OPC and 0.5% of CaCO3

10

0

0

20

0

0

30

0

0

40

0

0

50

0

0

60

0

0

70

0

0

80

0

0

90

0

1

100

1

2

110

2

4

120

3

6

130

6

-

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CALCULATIONS

Water content (%) =

 ___mass of water___  mass of cement

x 100%

 ______156____ ___  500

x 100%

(a) For OPC only, Water content (%) =

= 31% Hence, the water content for OPC to achieve the standard consistency test requirement is 31%.

(b) For composite cement (99.5% of OPC and 0.5% of CaCO 3), Water content (%) =

 ______158____ ___  500

x 100%

= 31.5% Thus, the water content for composite cement to achieve the standard consistency test requirement is 31.5%.

From the results and calculations, composite cement which consists of 99.5% of OPC and 0.5% of CaCO 3 requires more water than OPC cement to achieve the standard consistence of (6±2) mm.

DISCUSSION

In this experiment, there were two types of cement that were used in this experiment. They are ordinary portland cement (OPC) and composite cement. Composite cement is the mixture of 99.5% of OPC and 0.5% of calcium carbonate, CaCO3. In finding the standard consistency between the penetration value , each cement is weighed 500 g while the composite cement we used consists of 0.05% of  CaCO3 mixed with OPC cement .The standard consistency of the cement mixture must be in the range (6±2) mm. Based on the experiment that have been carried out , the result shows that in order to achieve the  penetration value needed according to BS EN (196-3:2005), 156 ml of water is required for the OPC cement and 158 ml of water is required for the composite cement. With the 156 ml of water mixed with OPC cement, the penetration reached 8 mm, meanwhile for the composite cement, the penetration is 7 mm. The results show that the composite cement needs more water than the OPC cement. 9

Besides that, the mineral admixture in the composite cement may also affect the water ratio needed. The mixtures such as the calcium carbonate, CaCO3 will donate to the addition in the water demand. The fineness of the CaCO3 will increase the water demand too. If there is excess water, the water will remain in the pores. Porosity will occur as water evaporates, leading to low strength. Contrarily, if less water is added, the cement will have poor workability and harden the concreting work. Hence, it is essential to use optimum volume of water by achieving the requirement of the standard consistency of cement.

In the experiment, the initial setting time is also determined. The quantity of water used is the same as the water used in testing the standard consistency within the penetration value. Based on the results obtained, there is a difference in the initial setting time between the composite cement and OPC cement. Composite cement takes shorter time to achieve the allowable penetration value which is between the value of 6 ±3 mm . The value of the penetration shows the distance of the needle and the base plate. The times taken to achieve this value for the OPC cement is 130 minutes meanwhile for the composite cement is 120 minutes . During the initial setting time, the OPC cement reached the penetration of 6 mm after 130 minutes and 6 mm for the composite cement after 120 minutes. Based on the result, the factors such as the quantity of the water content, fineness of the cement, temperature and humidity may affects the results obtained. Due to the cement mixture being manually mixed by hand, it may affect the results too as the rate of mixing might be different for each samples within the 3 minutes time. The higher the water content percentage, the longer the initial setting time is required for it to achieve the consistency. The hydration of the concrete will also increase if the temperature is high. Hence, it will reduce the setting time of concrete. The setting time will also decrease  proportionally with the increase of the fineness of cements with mineral admixtures. There are a few precautions needed to be aware of when carrying out the experiment. Owing to the wet cement paste being highly alkaline, gloves must be worn when mixing the cement with water to avoid direct contact to the skin. The Vicat plunger or needle is lowered gently until it contacts with the cement paste and pause in that position for few seconds to avoid initial velocity or forced penetration. This step is to prevent any inaccuracy in results obtained. Besides, cement paste should be compacted firmly to avoid any void and pores in the paste before Vicat test. The cement powder used should be well  preserved in room temperature and low humidity. An exposed to surrounding cement powder will affect its result. The experiment should be performed away from vibrations and other disturbances and should  be done in optimum room temperature and humidity not more than 50%. Observer should avoid parallax error when measuring the volume of water by using the measuring cylinder. 10

CONCLUSION

From the experiment, we discovered that the amount of distilled water required by OPC and composite cement which consists of 99.5% of OPC and 0.5% of calcium carbonate to achieve the standard consistency is different. We have carried out 2 trials until we obtained the allowable standard consistent which is (6±2) mm for the cement mixtures. OPC requires 156ml of distilled water to produce a distance between plunger and the base plate of (6±2) mm. In contrast, composite cement requires 158ml of distilled water to achieve the requirement of the standard consistency. Both cement mixtures require similar amount of water but still composite cement has higher water demand than OPC cement. The reason is due to the fineness and the surface area of the calcium carbonate added. Hence, slightly more water is needed for the composite cement to achieve the standard consistency. The initial setting time using the same water content stated above for OPC is 130 minutes whereas the composite cement requires 120 minutes to set. The distance between the needle and the base  plate for both cement mixtures is 6mm which is within the range of (6±3) mm. This means that the composite cement sets faster than the OPC cement. In other words, adding calcium carbonate into the cement mixture accelerates the setting time of the cement. As a result, early strength will become higher. Therefore, the composite cement is suitable to be used in the repairing works and in extreme cold weather conditions as it can be used to offset the retarding effect of low temperature. In short, with the addition of 0.5% of calcium carbonate into the OPC cement will accelerate the initial setting time.

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