Showing posts with label Problems in Civil Engineering. Show all posts
Showing posts with label Problems in Civil Engineering. Show all posts

Mixing and Batching of Mortar And Concrete Ingredients

ABSTRACT:
A concrete plant, also known as batch plant is device that combines various ingredients to form concrete. In general, it is a process of combining all ingredients of concrete as per the mix design. Batching and mixing are extremely important parts of mortar and concrete manufactures they influence properties of concrete both in plastic as well as in hardened stages. Also, it is one of the important processes, which is to be done to obtain a quality concrete. Many processes are carried out in various parts of the world with many changes and different equipment. There are various types of batching and mixing equipment and methods that is to say from manual to most sophisticated computerized batching and mixing. Mechanization improves quality of batching and mixing, its speed and thereby can most often result in economy.There are number of factors which are to be considered while doing the process which are discussed in this paper. Moreover, the machinery, which is to be required while making concrete or for batching process and discharging and unloading of the mixture, are also discussed in brief.

1.0 INTRODUCTION:
Concrete is the most widely used construction material in the world. This material is not going to be easily replaced by any other material on account of its economical as well as the technical advantage.This material is generally produced at the site in our country and therefore needs to be carefully supervised and controlled in order that it performs the way it is technically expected to perform.
Concrete is made from raw materials such as cement, natural and manufactured aggregates, water and at times concrete additives (chemicals). It is worth noting that cement and aggregates are manufactured or obtained from natural solid stone, which is quarried, crushed, screened and processed to give the required physical and chemical properties.
This paper covers the batching and mixing process of concrete manufacture. The processes of batching and mixing of concrete or mortar materials are very similar to preparations of a dish in cookery as per a recipe wherein various ingredients depending on their individual properties have to be mixed in correct proportions to give the required flavour and taste.

Plastic Cracking of Concrete

1.0 INTRODUCTION:
Cracking is one of the major issues in concrete. Since concrete has various physical and chemical properties it is prone to cracking. Its elimination is not possible totally but it can be restricted or reduced to a certain extent. Mostly, cracking goes on a microscopic scale and does not appear visibly as a fault. If the cracking goes on a macroscopic scale it can result in loss of strength, stability and durability. It can also cause decrease in sound insulation and overall efficiency besides affects aesthetics to a greater extent.
The main causes of cracking are as follows:
  • Ageing – Carbonation
  • Foundation problems
  • Weathering Actions
  • Improper or modified use of the structure
  • Poor maintenance
  • Progressive loading
  • Deficiencies in design
  • Poor quality of concrete material
  • Improper concrete mix
  • Movement of concrete arising from physical properties
  • Poor workmanship and negligence
  • Over troweling and impermeable formwork
  • Reduced continuity of the structural member
  • Defects and errors in construction practices
  • Improper structural repairs or modification
  • Chemical attacks by Chlorides and Sulphates
  • Differential thermal stress – Heat of hydration of cement

Since, prevention is better than cure it is always preferable to prevent cracking to a certain or a possible extent than to think of repairs in the future due to various reasons. One of the frequent occurrences of cracking of concrete is due to plastic shrinkage of plastic settlement. This paper deals with various aspect of these types of cracking.
2.0 OCCURRENCE OF PLASTIC CRACKING:
Both plastic shrinkage and plastic settlement cracks occur within a few minutes or hours of concrete placing and finishing. They occur when concrete is still in plastic state and has not fully hardened. They can be seen as early as 10 minutes from the time of placing and finishing to as late as 3 hours after placing.
The plastic cracks are of two types:
1. Plastic settlement Cracks
2. Plastic shrinkage Cracks