Jan 23 2014

Hot Weather Concreting

Hot weather can also be damaging to concrete. The fresh mix will require more water than usual to achieve the required slump and workability, will set faster and have reduced working time, will more likely experience plastic shrinkage cracking on the surface, and will suffer variations in air content. The hardened concrete will have lower strength, more drying shrinkage and tendency to crack, less durability in freeze thaw exposures, and less uniform surface appearance. The adverse effects of hot weather increase as temperatures rise, relative humidity falls, and wind increases, and the damage can never be completely undone. There are, however, a number of recommendations which can help avoid problems. The following protective measures should be taken when temperatures are 90°F or above, especially when accompanied by windy conditions or relative humidity below 25%.

To decrease the possibility of plastic shrinkage cracking, use the largest size and amount of coarse aggregate compatible with the job requirements and, if ordering from a ready mix supplier, specify a water reducing admixture.
Locate control joints at slightly closer intervals than when concreting in milder temperatures, and plan the locations of construction joints ahead of time with smaller working areas in mind.
Use sunshades or windbreaks as appropriate, and avoid working during the hot afternoon.
Have enough workers on hand to keep the job running smoothly and quickly.
If you are mixing concrete on site, sprinkle aggregate stockpiles ahead of time for evaporative cooling and use ice as part of the mixing water.
Reduce the time between mixing and placing as much as possible and avoid excessive mixing. Do not add water to ready mixed concrete at the job site.
Moisten the forms and reinforcement and moisten soil sub grades before placing the concrete.
Cure the concrete for at least three days, but preferably for one week. When forms are removed, provide a wet cover for newly exposed surfaces.

The primary concern of hot weather concreting is the rapid loss of mixing water to evaporation. All of the protective measures outlined are aimed at preserving the moisture needed for cement hydration and curing. If adequate moisture can be maintained in the concrete for at least three and preferably seven days, there will be no decrease in the quality of the concrete compared to that placed and cured in milder weather.

Jan 7 2014

Characteristics of good brick

The essential requirements for building bricks are sufficient strength in crushing, regularity in size, a proper suction rate, and a pleasing appearance when exposed to view.

Size and Shape: The bricks should have uniform size and plane, rectangular surfaces with parallel sides and sharp straight edges.

Color: The brick should have a uniform deep red or cherry color as indicative of uniformity in chemical composition and thoroughness in the burning of the brick.

Texture and Compactness: The surfaces should not be too smooth to cause slipping of mortar. The brick should have pre compact and uniform texture. A fractured surface should not show fissures, holes grits or lumps of lime.

Hardness and Soundness: The brick should be so hard that when scratched by a finger nail no impression is made. When two bricks are struck together, a metallic sound should be produced.

Crushing Strength: should not be less than 10 N/mm2

Brick Earth: should be free from stones, crushed stone, sand, organic matter, saltpetre, etc.

Jan 5 2014

Principal Properties of Building Materials

Building materials have an important role to play in this modern age of technology. Although their most important use is in construction activities, no field of engineering is conceivable without their use. Also, the building materials industry is an important contributor in our national economy as its output governs both the rate and the quality of construction work.

There are certain general factors which affect the choice of materials for a particular scheme. Perhaps the most important of these is the climatic background. Obviously, different materials and forms of construction have developed in different parts of the world as a result of climatic differences. Another factor is the economic aspect of the choice of materials. The rapid advance of constructional methods, the increasing introduction of mechanical tools and plants, and changes in the organization of the building industry may appreciably influence the choice of materials.

Due to the great diversity in the usage of buildings and installations and the various processes of production, a great variety of requirements are placed upon building materials calling for a very wide range of their properties: strength at low and high temperatures, resistance to ordinary water and sea water, acids and alkalis etc. Also, materials for interior decoration of residential and public buildings, gardens and parks, etc. should be, by their very purpose, pleasant to the eye, durable and strong. Specific properties of building materials serve as a basis for subdividing them into separate groups. For example, mineral binding materials are subdivided into air and hydraulic-setting varieties. The principal properties of building materials predetermine their applications. Only a comprehensive knowledge of the properties of materials allows a rational choice of materials for specific service conditions.

Jan 2 2014

Planning Suitable Building Orientation

Orientation means setting out the plan of the building with respect to north-south and east-west directions to provide an opportunity to user to enjoy sun-shine and breeze when required and to avoid the same whenever not required. This is also known as planning the aspect of a building. Aspect means arrangement of doors, windows in the external wall to make good use of nature. This term has nothing to do with the architectural aspect of outlook of building. Kitchen should have eastern aspect to enjoy morning sunshine, means, kitchen should be located on the eastern side of the building to make use of morning sun rays.

Dec 17 2013

Properties of Concrete

What Are The Properties of Concrete?

Most people commonly use the words cement and concrete interchangeably. It’s important to note that cement is only one component of three concrete properties and the term “concrete” is a mixture of the three.

Concrete properties consist of three basic components: water, aggregate (rocks and sand), and portland cement. Cement, usually in powder form, acts as a binding agent when mixed with water and aggregates.

This combination or mixture, when poured, hardens into this durable material called concrete that we are all familiar with.

The Three Basic Components of Concrete

1. Portland Cement – The cement and water form a paste that coats the aggregates and sand in the mix. The paste hardens and binds the aggregates and sand together.

2. Water – Water is needed to form a chemical reaction with the cement (hydration) to form heat. This starts the drying and hardening process. Water is also used to provide workability with the concrete.

The amount of water in the mix in pounds compared with the amount of cement is called the water/cement ratio. The lower the w/c ratio the stronger the concrete.

3. Aggregates – Sand is the fine aggregate and crushed stone and gravel are the coarse aggregate. These two materials help strengthen the concrete.

Some Desired Properties of Good Concrete

1. A workable mix that is easy to place and consolidate.

2. A high quality concrete using the lowest water-cement ratio possible, using the proper size coarse aggregate practical for the job you’re doing, using the optimum ratio of fine to coarse aggregate.

3. For hardened concrete resistance to freezing and thawing, deicing chemicals, wear resistance, strength, and low permeability (water tightness).

These are the basics of concrete properties to produce a concrete mix. There are other admixtures that are added to improve workability, durability, and set times.

Nov 28 2013

Curing of concrete

Curing of concrete is one of the essential requirement of process of concreting. Curing is process of keep the set concrete damp for some days in order to enable the concrete gain more strength.

Purposes:

Curing protects concrete surfaces from sun and wind
Presence of water is essential to cause the chemical action which a companies the setting of concrete

Nov 4 2013

Sand

Sand is an important building material used in the preparation of mortar, concrete, etc.

Sources of Sand: Sand particles consist of small grains of silica (Si02). It is formed by the decomposition of sand stones due to various effects of weather. The following are the natural sources of sand.
Pit Sand: This sand is found as deposits in soil and it is obtained by forming pits to a depth of about 1m to 2m from ground level. Pit sand consists of sharp angular grains, which are free from salts for making mortar, clean pit sand free from organic and clay should only be used.
Rive Sand: This sand is obtained from beds of rivers. River sand consists of fine rounded grains. Color of river sand is almost white. As the river sand is usually available in clean condition, it is widely used for all purposes.
Sea Sand: This sand is obtained from sea shores. Sea sand consists of rounded grains in light brown color. Sea sand consists of salts which attract the moisture from the atmosphere and causes dampness, efflorescence and disintegration of work. Due to all such reasons, sea sand is not recommendable for engineering works. However be used as a local material after being thoroughly washed to remove the salts.

Jun 4 2013

Rolled Concrete

Rolled concrete is concrete which is placed with standard (asphalt) road pavers and is then levelled and compacted with smooth coated vibrating rollers. Rolled concrete is used mainly in the construction of hard standing, large surfaces (car parks) and road surfaces. The concrete composition is similar to standard concrete. Semidry consistence: Crushed material is preferable for good green strength.

The coarse material, sand, binder (standard cement) and water content must be coordinated. In particular, the water content must be kept constant and precise to allow the voids to be filled as fully as possible by rolling.