Test for Clay Lumps and Friable Particles Purpose Clay and friable particles may be present in the form of lumps in natural aggregates. If they are near the surface, these lumps can cause pitting under the influence of traffic. Specifications frequently limit these particles to a maximum of 1%. Equipment and Materials Weighing device accurate … Read more
Compressive Strength Test of Hydraulic Cement Mortar Purpose The following covers only that portion of ASTM Designation: C 109 that is required to determine the compressive strength of 50 mm (2 inches) of Portland cement mortar cubes. Equipment and Materials A 2kg scale accurate to 0.1 gram Six 50 mm (2 inch) cube molds Hard … Read more
Advantages of Prestressed Concrete Most of the prestressed members are precast and therefore all the advantages or precast concrete hold true for prestressed concrete also. To know the advantages of precast concrete click here. In addition, there are advantages to be gained by prestressing when conditions are favorable to its use. Following additional advantages due … Read more
Placing of Concrete in Hot Weather For normal concreting operations the temperature of concrete should vary between 150C to 250C to enable it to attain its full ultimate strength within 28 days. In case concreting is carried out in extreme hot weather conditions, the rate of hydration of cement gets accelerated and the water in … Read more
Yield of Concrete There are various factors which affect the yield of concrete for a given proportion of concrete ingredients, such as Water-cement ratio Size of aggregate Method of compaction etc. Yield of concrete simply means the actual volume of concrete produced when a given proportion of concrete ingredients are mixed in a certain manner. … Read more
Concrete Placing Precautions The concrete, as it comes out of the mixer or as it is ready for use on the platform, is to be transported and placed on the formwork. Following precautions should be taken during placing of concrete. The formwork or the surface which is to receive the fresh concrete should be properly … Read more
Concrete for long have been specified by nominal mixes (mixes of fixed proportions which ensure adequate strength) and were arbitrarily applied with little regard to the required strength of concrete with water added to ensure workability. But for mixes of desired strength the three variable factors to be considered are: Water cement ratio and consistency … Read more
Vibrators are commonly used as a way of compacting concrete on site. In case of vibration, compacting gets effected by reduction in internal friction between various particles of concrete due to oscillation of particles which results in a dense and compact mass of concrete. Vibrations can either be Produced in the interior of the concrete … Read more
Surface Index of Aggregates Surface index of aggregates is another way to represent the specific surface of aggregate. This method was suggested by Murdock. Murdock provided some empirical numbers to represent the specific surface of different aggregates grading (as shown in the table below). Surface Index Values for Single Graded Aggregate TABLE-1 Sieve Size Within … Read more
Plastic shrinkage cracking (as shown below) is caused by rapid drying of the concrete surface. They can occur at any time of the year, from cooler low-humidity weather conditions to, in particular, hot weather conditions involving any one or a combination of high temperature, low humidity and wind. These types of cracks occur while the … Read more