Cement and Types of Cements...

Cement and Types of Cements Any substance which bonds materials is normally considered as cement. There are many types of cements. However in construction, the term cement generally refers to bonding agents that are mixed with water or other liquid, or both, to produce a cementing paste. Initially, a mass of particles coated with the paste is in a plastic state which can be formed, or moulded, into various shapes. Such a mixture is normally considered a cementitious material since it can bond other materials together. After a time, due to chemical reactions, the paste sets and the mass harden. When these particles consist of fine aggregate (sand) then mortar is formed. When these particles consist of fine and coarse aggregates then concrete is the result. In its simplest form, concrete is a mixture of paste and aggregates. The paste, composed of portland cement and water, coats the surface of the fine and coarse aggregates. Through the chemical reaction which is called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete. Within this process lies the key to a remarkable trait of concrete is that it is plastic and malleable when newly mixed, strong and durable when hardened. Concrete’s durability, strength and relatively low cost make it the backbone of buildings and infrastructure worldwide houses, schools and hospitals as well as airports, bridges, highways and rail systems. It is the most-produced material on the mother earth. Even construction professionals sometimes incorrectly use the terms cement and concrete interchangeably. Cement is actually an ingredient of concrete. It is the fine powder which, when mixed with water, sand, and gravel or crushed stone (fine and coarse aggregate), forms the rock-like mass known as concrete. Though the history of cementing materials is...

Components of Product Quality Management...

Components of Product Quality Management Product quality is the group of features and characteristics which determines the capacity of the product to meet the specification requirements of a standard or of a customer. It is often defined as ‘the ability to fulfill the customer’s needs and expectations’. It is also sometimes defined as ‘meeting specifications at the lowest possible cost’ as well as ‘delivering the value that a customer derives from a product’. It is important for the organization that the quality products are delivered to the customers since they are the top most drivers for the organizational success. After all, growing sales make the foundation of the organizational performance not only to remain consistent but also make it strong and sturdier. However, in the organization, employees do make mistakes and machines and equipment do have breakdowns. The goal of the product quality management is to minimize this so that the customer remains happy with the product performance and reorders the products. For this the organization is to put a relentless focus on product quality. Improving product quality save the organization the cost since it needs not to do things to cover up old mistakes. Improving quality also raises the employees’ engagement since they like to be on a high performance team. Product quality management includes the following four major components. They are (i) quality planning, (ii) quality control, (iii) quality assurance, and (iv) quality improvement. Quality planning Quality planning is the process for ‘identifying which quality standards are relevant to the product and determining the procedures and techniques to satisfy them’. Quality planning means how to fulfill the process and deliverable products quality requirements. It helps the organization to schedule all of the tasks needed to make sure that the products meets the...

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking Sep23

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking...

Welding of Carbon and Low Alloy Steels and Hydrogen Induced Cracking Arc welding is a process by which steels are joined by coalescence. Normally the process uses a compatible filler material. Before a well-bonded joint is produced, the joint surface is to be heated above the melting temperature in order to completely fuse with the weld metal. Though the metallurgical reactions which involve melting, solidification, and solid-state transformation are not unusual, the temperatures and cooling rates observed are severe. Active gases also are present and can dissolve in the fused steel. Fluxes are introduced to alloy with and protect the weld metal. Generally, joints are rigid and restrain dimensional changes caused by shrinkage and solid-state transformations, producing residual stresses of yield-strength (YS) magnitude. Since the metallurgical changes do not occur under equilibrium conditions, and since the stresses are high, many of the reactions can take place in either or both the weld metal and the heat affected zone (HAZ) of the steel and can produce defects that weaken their soundness. Because of the tremendous variability of the welding processes, it is difficult to provide much detail about the exact mechanisms involved or the corrections that can be made. Furthermore, many corrective measures are obvious once most defects are explained. One problem, which relates to hydrogen (H2), is not simple. Since this problem is becoming more relevant as more high-strength, low-alloy (HSLA) steels are being welded, the subject of hydrogen-induced cracking (HIC) is very important. Carbon (C) and low alloy steels are welded since they have widespread application and good weldability. This usefulness is mainly due to the metallurgical characteristics of the iron (Fe) base system. The characteristic includes the ability to undergo allotropic (microstructural) transformation which allows the opportunity for hardening and strengthening through...