Overview Blaine’s air permeability apparatus consists essentially of a means of drawing a definite quantity of air through a prepared bed of cement of definite porosity. The fineness is expressed as a total surface area in square centimeters per gram. Apparatus Measuring instruments Name Range Accuracy Blaine air permeability apparatus Refer to IS:5516 Balance 3 … Read more
Objective Determination of initial and final setting time of concrete as per IS-8142-1976. Apparatus • Non absorptive metal container having minimum lateral dimension of 150 mm and minimum depth of 150 mm. • Penetration resistance apparatus having a pressure gauge of capacity 700 to 900 N. Removable needles of 645, 323, 161, 65, 32 & … Read more
To get better efficiency, the sequence of charging the loading skip is as under 1. First place half the quantity of coarse aggregate in the skip. 2. Place half the quantity of fine aggregate over the previously placed coarse aggregate. 3. Then pour full quantity of cement (i.e. one bag of cement) over it. 4. … Read more
For preparation of special products like precast concrete membranes, some special compaction methods are used, such as • Vibropressing • Shock • Centrifugation • Air jets Vibropressing Compacting in this method is effected by applying external pressure on top and vibrating from bottom. Table vibrators are usually made use of in this process. This process … Read more
The following properties of aggregate affect the properties of hardened concrete. 1. Grading Aggregate grading has no significant effect on the properties of hardened concrete. 2. Bulk Density This has no direct effect but has an indirect effect on drying shrinkage. Bulk density is an indicator of packing capacity, which influences water requirement, which in … Read more
Grading In case of sands, it has been found that materials having a large deficiency or excess of any size fraction adversely affect the workability of concrete. The most important size fraction in a concrete sand are those passing the 0.30, 0.15 and 0.075 mm sieves. If these fractions are too low the concrete tends … Read more
What is a Poker Vibrator? A poker vibrator consist of an electric weight encased in a housing and may be driven by an electric or pneumatic motor or a petrol or diesel engine. Poker diameters range from 25 to 75 mm. How To Use Poker Vibrator? A poker vibrator should be used as follows Insert … Read more
Objective To determine quantity of silt in fine aggregates in the field Theory There are two types of harmful substances preset in fine aggregates i.e. organic matter produced by decay of vegetable matter and/or clay and silt, which form coating thus preventing a good bond between cement and the aggregates. If present in large quantities, … Read more
What is Contraction Joints ? Contraction joints are planes, usually vertical separating concrete in a structure or a pavement placed at a designed location. Contraction joint is placed in such a way that it interferes least with the performance of the structure as well as prevents formation of objectionable shrinkage cracks elsewhere in concrete. Why … Read more
The aggregates should be stored near the mixer A clean dry and hard surface should be selected for the storage. Aggregates should not be dumped on loam or grass. In the absence of clean and hard surface a platform constructed of wooden planks, old iron sheets, bricks or lean cement concrete may be used. During … Read more
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