Paddy Engineering Consultant

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 to be prone to segregation. A rule of thumb guideline for optimum percentage is 30%, 15% and 7.5% respectively passing the 0.30 mm, 0.15 mm and 0.075 mm sieves. The percentage passing the 0.075 mm sieve may be used as a first estimate of the concrete’s tendency to bleed -the greater this fraction the lower the bleeding. BULK DENSITY Bulk density is a measure of aggregate packing capacity and therefore influences water requirement and mix proportioning. It does not have a direct influence on workability, provided the mix is correctly proportioned. PARTICLE SPECIFIC GRAVITY Because bleeding and settlement are driven by the force of gravity, the higher the specific g...

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 turn influences drying shrinkage of hardened concrete. For a given particle specific gravity, the higher the bulk densities of sand and stone, the lower the water requirement and hence the lower the drying shrinkage. 3. PARTICLE SPECIFIC GRAVITY Because aggregates make up about 80% of the mass of concrete, particles specific gravity of aggregates significantly affects the density of the concrete. 4. PARTICLE SHAPE Angular, flat and elongated stone particles tend to increase the flexural strength of concrete. The effect of particle shape on compressive strength is negligible. 5. SURFACE TEXTURE Rou...

PROPERTIES OF MORTAR Properties of mortar which are sought for use in masonry are: workability, water retentivity, rate of stiffening, strength, resistance to rain penetration and durability. These properties have been discussed below explaining their effect on masonry. Choice of masonry mortar is governed by several considerations such as: Type of masonry unit and its properties, Degree of exposure to weather and environments, Strength requirements, etc. 1.  WORKABILITY Workability is the property of mortar which enables it to be spread and applied to masonry unit with ease. It also facilitates proper filling of joints in masonry. A good mortar would hang from the trowel and will flow down readily when lightly jerked. This property of mortar depends on properties of various ingredients used for making mortar and on the method of mixing adopted. As a general rule, a mud mortar prepared from fine clay soil has better workability than one prepared from sandy soil and a lime mort...