Experiment no 03 setting time of cement.
- 1. ENGINEERING MATERIALS LABORATORY ENGR.SAYED SHAJEDUL HASAN. EXPERIMENT NO: 03 THE DETERMINATION OF THE INITIAL AND FINAL SETTING TIME OF THE CEMENT BY VICAT NEEDLE APPARATUS.
- 2. ENGINEERING MATERIALS LABORATORY ENGR.SAYED SHAJEDUL HASAN. INTRODUCTION: Setting time of cement: When cement is mixed with water, it hydrates and makes cement paste. This paste can be molded into any desired shape due to its plasticity. Within this time cement continues with reacting water and slowly cement starts losing its plasticity and set harden. This complete cycle is called Setting time of cement. Initial Setting time of Cement: The time at which cement starts hardens and completely loses its plasticity is called Initial setting time of cement. Final setting time of Cement: The time at which cement completely loses its plasticity and became hard is a final setting time of cement. USE OF SETTING TIME OF CEMENT: Initial setting time of cement is important, to know when the cement is starting to lose its plasticity. It is helpful in determining the time needed for the concreting process, i.e. transportation, placing and compaction of concrete. Final setting time of cement is important to know when the cement would be set. This testing of cement is helpful to determine safe removal time of side of form (not vertical support) or scaffolding of concrete. SCOPE & SIGNIFICANCE: This test method is used to determine the time of setting of the hydraulic cement by VICAT needle apparatus. The knowledge of the setting time of the cement is always helpful in deciding the time duration to mix, transport, place and compact the concrete effectively. We always prefer a larger initial setting time so that we can mix, transport and place the concrete easily. According to ASTM specifications, the initial setting time shall not be less than 45 min but in the field we prefer an initial setting time not less than 90 min. A smaller value of the final setting time is always preferred in order to avoid large expenditures on the formwork. According to most of the specifications, the final setting time shall not be greater than 10hrs and shall not be less than (90 + 1.2 x (initial setting time)) min. FACTORS THAT AFFECT INITIAL AND FINAL SETTING TIME OF CEMENT: - The fineness of cement, the presence of salts in sand, atmospheric conditions. For example, cement requires a temperature of 27°c to complete Hydration, during winters the climate is low which stops the hydration and takes a longer time to set harden.
- 3. ENGINEERING MATERIALS LABORATORY ENGR.SAYED SHAJEDUL HASAN. APPARATUS VICAT apparatus Needle of 1mm2 cross-section and 50mm length (for initial setting time) Plunger with 1mm smaller needle and 5mm outer diameter (for final setting time) Flat trowel Graduated cylinders & Enamel tray Stop watch Balance
- 4. ENGINEERING MATERIALS LABORATORY ENGR.SAYED SHAJEDUL HASAN. TEST PROCEDURE Initial Preparation Consistency test to be done before starting the test procedure to find out the water required to give the paste normal consistency (P). Take 250 g of cement and prepare a neat cement paste with 0.85P of water by weight of cement. Gauge time is kept between 3 to 5 minutes. Start the stop watch at the instant when the water is added to the cement. Fill the Vicat mould, resting on a glass plate, with the cement paste gauged as above. Fill the mould completely and smooth off the surface of the paste making it level with the top of the mould. The cement block thus prepared is called test block. The mould may be slightly shaken for remove the air. Initial Setting Time of Cement Place the mould under the rod bearing the needle. (needle for determining the initial setting time) Lower the needle slightly until it comes in contact with the surface of the test block and quickly release, allowing it to penetrate the test block. In the starting, the needle will completely penetrate the test block. Repeat this procedure until the needle fails to penetrate the block to the 5 to 7 mm from the bottom of the mould. The period elapsing between the time when water is added to the cement and the time at which the needle fails to penetrate the test block to the 5 to 7mm from the bottom of the mould is called the initial setting time. Final Setting Time of Cement To determine the final setting time, the first needle is replaced by the (needle for determining the final setting time) needle with an annular attachment. When applying the needle gently to the surface of the mould, the needle makes an impression thereon. Cement called as final set while the attachment fails to make an impression on the surface of the test block. The period elapsing between the time when water is added to the cement and the time at which the needle fails to make an impression on the surface of the test block is called the final setting time.
- 5. ENGINEERING MATERIALS LABORATORY ENGR.SAYED SHAJEDUL HASAN. CALCULATIONS Initial setting time: Time when needle fails to penetrate 5 mm to 7 mm from bottom of the mould-Time at which water is first added to cement. Final setting time: Time when the needle makes an impression but the attachment fails to do so - Time at which water is first added to cement. OBSERVATION: Sample brand: Holcim Cement Room temperature :28°c Normal Consistency: 33% Weight of cement: 250gms Water added: 70. 5 ML Time when water is added to cement 10:35 am Time at initial setting 12:30 pm Initial setting time,(min) 115 min. Time at final setting 2:20 pm Final setting time,(min) 226 min RESULTS: Initial setting time: 115 min. Final setting time: 226 min The results of the initial and the final setting time should be reported to the nearest five minutes. COMMENTS: After performing the experiment, we have concluded the results that the initial setting time of cement is 115 min and final setting time of cement paste is 226 min. The minimum initial setting time is 30 minutes and maximum final setting time is 600min. As the Initial and Final setting time is coming in between the prescribed range, it means that the experiment is performed accurately. SIGNATURE
- 6. ENGINEERING MATERIALS LABORATORY ENGR.SAYED SHAJEDUL HASAN. ACCEPTANCE CRITERIA: Recommended result for various types of cement to their setting time gives by standard guidelines are as follows: If test value is not in a rage of the recommended result, there many reasons behind it, such that some chemical composition may have changed during production (manufacturing defect), fault in the testing apparatus, error in testing etc. In that case, have to take care of the timing of work with it. If the initial setting time less than this value, all the process, i.e. mixing, transporting, placing complete within the time otherwise cement paste/concrete/mortar starts to getting set. If the final setting time is more than this value, will have to retain scaffolding and the sides of the form, until the cement paste/concrete/mortar is completely rigid and will have to be careful to start the curing time.