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Some of the features on CT. Find a vaccination site near you at ct. Visit us today! The information obtained from fineness modulus is helpful in the following ways; 1- Fineness modulus tells us directly whether the material is well-graded or gap- graded. Lower the surface area of the aggregate, the required amount of fresh cement paste to cover the aggregate particles will be less and thus less water is required. For a good fine aggregate, the FM should be between 2. It is a single factor or an empirical number which we get from the results of sieve analysis.
The value of FM will not change if we add sieves above. OR It is the operation of determining the particle size distribution of the given specimen. This gradation gives an indirect measure if the workability and average particle size.
Take the minimum and the maximum values provided by ASTM and plot them on the grading curve. Now take these minimum and maximum value lines as your reference and if the curve of our own data lies inside these two lines then the quality of our sample is OK but if your curve lies outside these two lines of maximum and minimum range then the sample is not according to specifications.
The sample should be perfectly dry because if there is some moisture content present then the particles will stick together and will not pass through the sieves. The pan is placed at the bottom-most position. The manual method should be performed in a proper sequence which is as follows; i- forward and backward motion ii- left and right motion iii- clockwise CW and counter-clockwise CCW motion iv- Frequent jolting. Time elapsed for the sieving process is minutes. Weigh the mass retained on each sieve and calculate the percentage passing through each sieve.
Mechanical Sieve Shaker During the concrete mix design, when the aggregate is to be batched by volume or by weight, then it becomes necessary to know the mass of the aggregates that will fill the container of unit volume. If we know the bulk density of the aggregate material then we can easily determine the mass required to fill a unit volume container. Bulk density also indicates the percentage of voids present in the aggregate material.
This percentage of voids affects the grading of the aggregates which is important in high strength concrete. Bulk density also indicates the compactive effort required to compact the concrete. The term volume includes the volume of the individual particles and the volume of the voids between the particles.
Bulk density is used in weight and volume batching. VOIDS It is the space between the individual particles in a unit volume of the aggregate mass and is not occupied by the solid mineral matter. Voids within the particles, either permeable or impermeable are not included in the voids for the determination of bulk density by this method. It also depends upon the size, distribution and shape of the particles. If the particles are of the same size, then it can be packed to a limited extent but when the smaller particles are added, the voids get filled with them and thus the bulk density increases.
For a coarse aggregate, a higher bulk density means that there are few voids which are to be filled by the fine aggregate and cement. Thus bulk density also depends upon the degree of packing. For the determination of the loose bulk density, fill the container with the aggregate material by means of a shovel and level its top surface. Weigh the container filled with the aggregate and note down its reading.
Then the loose bulk density of the aggregate material can be computed by using the relation; Now for the determination of the compacted bulk density, the only difference is in filling the container.
In this case, the container is filled in three equal layers. Fill the container about one-third full and level the surface with the fingers. Rod the layer of the aggregate with 25 strokes of the temping rod evenly distributed over the surface. Next fill the container two-third full and again rod it with 25 strokes of the temping rod.
Finally, fill the container to overflowing and rod again in the manner previously mentioned. Now level the top surface and weigh the container.
The information obtained from specific gravity is helpful in the following ways; 1- The knowledge of the specific gravity is important for the concrete technologist to determine the properties of concrete made from such aggregates. If the aggregate is to be batched in the dry condition, then it is assumed that sufficient amount of water will be absorbed from the mix to bring the aggregate in the saturated condition.
If an additional amount of water is not added as a cover for the absorbed water, the loss of workability is resulted. Limitation The limitation of the test is that, it can not be used for the light weight aggregates. The term absorption does not include the amount of water adhering to the surface of the particles.
Water absorption is expressed as percentage of the dry mass. CONDITION It is the condition related with the aggregate particles in which the permeable pores of the aggregate particles are filled with water but without free water on the surface of the particles. The term volume includes the volume of the permeable and the impermeable pores and does not include the volume of the voids between the particles. The term volume includes the volume of the permeable and the impermeable pores which are filled with water and does not include the volume of the voids between the particles.
OR It is the mass per unit volume of the solid portion of the particles excluding the voids. Remove the test sample from the water and roll it in a large absorbent cloth until all visible films of water are removed. Wipe the larger particles individually. A moving stream of air is permitted to assist in the drying operation. Take care to avoid evaporation of water from aggregate pores during the surface-drying operation. Determine the mass of the test sample in the saturated surface-dry condition.
Record this and all subsequent masses to the nearest 0. Take care to remove all entrapped air before determining its mass by shaking the container while immersed. The difference between the mass in air and the mass when the sample is immersed in water equals the mass of water displaced by the sample.
The measure cup shall be filled about one-third full with the aggregate and gives 25 tamping rod. A further similar quantity of aggregate shall be added and a further 25 tamping given to the second and tot the last layer 25 tamping shall again be given and the surplus aggregate struck off using the tamping rod as a straight-edge.
The net weight of aggregate in the measure shall be determined to the nearest gram weight A and this weight shall be used for the duplicate test on the same material.
The cup shall be fixed firmly in position on the base of the machine and the whole of the test sample placed in it and compacted by a single tamping of 25 strokes of the tamping rod. The hammer shall be raised until its lower face is 15 in.
The test sample shall be subjected to a total 15 such blows each being delivered at an interval of not less than one second. The crushed aggregate shall then be removed from the cup and the whole of it sieved on No. The fraction passing the sieve shall be weighted to an accuracy of 0. Two tests shall be made. Results are calculated and reported as the modulus of rupture.
It is used in testing concrete for the construction of slabs and pavements. In direct tension test following are the difficulties: 1.
When concrete is gripped by the machine it may be crushed due the large stress concentration at the grip. Care shall be taken to keep the needle straight. COMMENTS: The factors influencing the setting properties of cement are its composition, the percentage of retardant, degree of calcination, fineness of grinding, aeration subsequent to grinding clinker, percentage of water used to make cement paste, the temperature of the mixing water, cement and the atmosphere where the cement paste is placed, and the amount of manipulation the paste receives.
Standard Sand: The standard sand to be used in the test shall conform to IS: or sand passing percent through 2 mm sieve and retained percent on 90 micron IS sieve. THEORY: The compressive strength of cement mortars is determined in order to verify whether the cement conforms to IS specifications and whether it will be able to develop the required compressive strength of concrete.
Strength test are not done on neat cement paste because of difficulties of excessive shrinkage and subsequent cracking of neat cement. Strength of cement is indirectly found on cement — sand mortar in specific proportion. The average compressive strength of at least three mortar cubes area of the face 50 cm2 composed of one part of cement and three parts of standard stand should satisfy IS code specifications.
The cubes are prepared for this purpose. Testing: 1 Take the cube out of water at the end of 3 days with dry cloth. Measure the dimensions of the surface in which the load is to be applied. For 3 days strength: Sl. For 28 days strength: Sl. COMMENTS: In addition to the effect of composition, the strength of cement is greatly influenced by the degree of burning, the fineness of grinding, and the aeration it receives subsequent to final grinding.
Under-burnt cement is likely to be deficient in strength. Compressive strength is the basic data required for mix design. By this test, the quality and the quantity of concrete can be controlled and the degree of adulteration can be checked. THEORY: The specific gravity of an aggregate is generally required for calculations in connection with cement concrete design work for determination of moisture content and for the calculations of volume yield of concrete.
The specific gravity also gives information on the quality and properties of aggregate. The specific gravity of an aggregate is considered to be a measure of strength of quality of the material.
Stones having low specific gravity are generally weaker than those with higher specific gravity values. The bulk density of an aggregate is used for judging its quality by comparison with normal density for that type of aggregate. It is required for converting proportions by weight into proportions by volume and is used in calculating the percentage of voices in the aggregate.
Find its weight W3. Find its weight W4 6 Repeat the same process for another trail by taking the aggregate up to the full of the container and by filling the water up to same point.
Description Trial 1 Trial 2 No. Weight of empty container W1 2. Weight of container with material W2 3. Take ml of dry sand V1 ml in clean measuring jar of ml capacity. Add a measured quantity of ml clean water to the above sample V2 ml i. Shake the jar thoroughly till all air bubbles are expelled.
Moisture forms a film around each particle and this film of moisture exerts surface tension which keeps the neighbouring particles away from it. Therefore, when no point contact is possible between the particles, this causes bulking of sand. Thus increase in volume of sand due to presence of moisture is known as bulking of sand.
When more water is added sand particles get submerged and volume again becomes equal to dry volume of sand. Fine sands show greater percentage of bulking than coarse sands with equal percentage of moisture. The points on the graph should be linked as a smooth curve. Then from the graph, maximum percentage of bulking and the corresponding moisture content is determined. COMMENTS: The bulking of the volume depends on the extent of surface tension and consequently how far the adjacent particles are kept away which in turn depends upon the percentage of moisture content and the particle size of the fine aggregate.
It is interesting to note that the bulking increases with the increase in moisture content up to a certain limit and beyond that the further increase in the moisture content results in the decrease in the volume and at a moisture content representing saturation point, the fine aggregate shows no bulking.
Due to the bulking, fine aggregate shows completely idealistic volume. Therefore, it is absolutely necessary that consideration must be given to the effect of bulking in proportioning the concrete by volume. If the effect of bulking is overlooked, in case of volume batching, the resulting concrete is likely to be under-sanded and harsh. It will also affect the yield of concrete for the given cement content.
Weighing balance Sensitivity 0. Coarse aggregate is broken stone used in concrete. The size of the fine aggregate is limited to maximum 4. Fineness modulus is only a numerical index of fineness, giving some idea about, the mean size of the particles in the entire body of concrete. Determination of fineness modulus is considered as a method of standardization of grading of aggregates i.
It is obtained by sieving known weight of given aggregate in a set of standard sieves and by adding the percent weight of material retained on all the sieves and dividing the total percentage by Carry out sieving by hand, shake each sieve in order 75mm , 40mm, 20mm, 10mm, and 4. Cumulative Sl. Retained Retained Passing retained 1.
The slump cone is a hollow frustum made of thin steel sheet with internal dimensions, as the top diameter 10 cms. The bottom diameter 20 cms, and height 30cms. It stands on a plane nonporous surface. To facilitate vertical lifting from moulded concrete it is provided with a suitable guide attachment and suitable foot pieces and handles.
The tamping rod is 16mm. This vertical settlement is called slump. Slump is a measure of workability. There are four types of slump- i. True slump refers to general drop of the concrete mass evenly all around without disintegration. Zero slump concrete is defined in the same document, as concrete of stiff or extremely dry consistency showing no measurable slump after removal of the slump cone.
Collapse slump indicates that concrete mix is too wet and the mix is regarded as harsh and lean. Shear slump indicates that the concrete lacks cohesion. It may undergo segregation and bleeding and thus is undesirable for the durability of concrete. For each mix take 2.
Cement, 5 Kg. Tamp each layer 25 times with tamping rod. Note: Slump test is adopted in the Laboratory or during the progress of the work in the field for determining consistency of concrete where nominal max. Any slump specimen which collapses or shears off laterally gives incorrect results and at this juncture the test is repeated only true slump should be measured.
For example, a harsh coarse mix cannot be said to have same workability as one with a large portion of sand even though they have the same slump. The upper mould has internal dimensions as top dia 25 cm D1 bottom dia.
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