Reactive Aggregate Ready for Reinforced Concrete?
The properties of the cement, aggregate and water will have a significant impact on the performance and durability of concrete. One of the most common reactive aggregates is pyritic shale. Pyritic shale is a fine-grained metamorphic rock that contains pyrite (FeS2). Pyrite oxidizes when exposed to water and air, creating sulphuric acid that can attack the cement paste and aggregate, leading to expansion, cracking, scaling and reduced durability. Cement paste exposed to sulphuric acid may also experience decreased strength, increased permeability and alkali-silica reactivity. The presence of certain minerals in the aggregate may intensify these effects.
The amount of pyritic material present in aggregates varies widely throughout Canada. For example, fine-grained precambrian metamorphic rocks such as those found in Southern Ontario can contain up to 10% pyrite by weight. These rocks are often crushed into coarse and fine aggregates used in concrete production. Field studies have shown that aggregates containing more than 3% pyrite by weight pose a risk if used in reinforced concrete construction because they will deteriorate rapidly after exposure to water and oxygen.
Various tests are available to
The properties you need to work with the material.
Reinforced concrete is heavy, has high compressive strength, and has low tensile strength. The steel reinforcing bar adds tensile strength to the concrete, thus making it much stronger.
Concrete is a very versatile material in terms of its ability to be mixed and molded into any shape or size. This ease of construction also makes it useful to repair. Concrete can be poured on top of existing concrete and be made to match the surrounding area seamlessly.
The most important property of concrete is that it is hard when dry and stays like that for years. There are no moving parts in reinforced concrete, so there is no wear and tear as there would be in a wooden structure or even a brick building. The only maintenance needed on a reinforced concrete structure is cosmetic repair of the surface where it was damaged by weather or impact.
What is Concrete?
Concrete is a composite material composed of aggregate bonded together with a fluid cement which hardens over time. Most use of the term “concrete” refers to Portland cement concrete. Concrete is one of the most versatile and durable building materials available in the world.
Concrete is made from a mixture of water, aggregate (rock, sand, or gravel) and Portland cement. Although several types of concrete exist, all concrete contains these four key ingredients which are mixed in varying quantities to create different strengths and consistencies.
Portland cement is the basic ingredient of concrete. It is a fine powder produced by grinding Portland cement clinker (more than 90%), a limited amount of calcium sulfate (which controls the set time) and up to 5% minor constituents as allowed by various standards such as the European Standard EN 197-1.
Portland cement clinker is made by heating a homogeneous mixture of raw materials in a rotary kiln at high temperature . The products of the chemical reaction aggregate together at their sintering temperature, about 1450 °C (2640 °F). The result is called “clinker” and it resembles small rocks or pebbles. Clinker typically comprises 3–20%
The majority of homes and other structures in the United States are constructed using reinforced concrete. But concrete is made of cement, water, and an aggregate such as sand or gravel. Cement and water form a paste that hardens and binds the aggregate together to form a matrix. The cement must be strong enough to withstand the stresses of the surrounding soil and water, while still being flexible enough to move with the ground without cracking.
Cement is used to make concrete because it can withstand stress. It has been used in buildings for hundreds of years. Today, cement is still used for building foundations, roads, bridges, dams, and other structures.
Concrete is usually made from crushed rock called aggregate mixed with sand or gravel. Sand or gravel are mixed into the concrete to help bind it together. Concrete contains cement but does not contain any sand or gravel. The crushed rock is mixed with water to form a mixture that can be poured like cement into molds.
Reinforced concrete is used in most modern buildings because it allows architects and engineers to design buildings that are durable, resistant to fire and water damage,and safe during earthquakes. It also provides a low-cost alternative to traditional materials such as wood or steel for many types of construction projects.
Portland cement concrete is a popular construction material that can be used in many different applications. These include concrete for foundations and slabs, for the exterior cladding of buildings, and for pavements. Concrete is strong in compression but relatively weak in tension. Reinforcing materials such as steel bars (rebar) are included to give concrete strength under tension. Concrete and rebar are combined together to form reinforced concrete.
Concrete has been used since Roman times, and while its composition has changed over time, its use continues to evolve. During the 1900s there was a rapid increase in the use of concrete worldwide, and it is now considered one of the most widely used building materials on earth. In fact, some estimates have the volume of concrete used globally each year at approximately 10 billion cubic meters.
Concrete is a mixture of aggregates combined with a paste of portland cement and water that hardens to an incredibly durable solid material. It is similar to mortar, but unlike mortar it is poured into place instead of being laid brick by brick or stone by stone. The aggregates typically used in portland cement concrete are sand, gravel or crushed stone; the paste is water and portland cement. Portland cement is manufactured by heating limestone or chalk with clay in
The history of concrete is a very long one, and it does not start in the 1830s as is commonly supposed. The ancient Romans were probably the first to use concrete; they used lime mortars and aggregates of broken brick or stone in their structures. Their concrete production techniques and formulas have been lost in time, concealed by the passage of centuries.
The early Egyptians made bricks from sand and clay, but there are no traces of concrete construction on their monuments. It is thought that they may have discovered the method for making hydraulic cement by accident when they found that ashes poured into water hardened into lumps. There is no evidence of any major use of this substance, however.
The ancient Greeks had a light natural aggregate that was volcanic tuff, formed by the explosion and solidification of gases in ancient volcanic activity. They did not make use of it in any extensive construction work, but there are some traces of mortar fragments with this material as an aggregate.
The Chinese used a type of cementitious material, called pozzolana, which was composed mainly of slaked lime and ash from burned rice hulls and other organic materials, such as fish waste. In India, natural deposits of pozzolana were also used for similar purposes.
In the past 6 years the industry has transformed from a local market to a globalized business, with more than 50% of all cement consumed in the United States being imported.
The industry is also characterized by several trends and mega-trends that will shape its future. These include:
* Increased globalization in the markets for inputs and outputs;
* Rising consumption in emerging economies;
* Sustainability issues related to energy consumption and CO2 emissions;
* The need for increased capital investments due to regulatory changes;
* Demographics and changes in working conditions.