When deciding whether or not to use lightweight concrete, a buyer needs to understand that this type of material isn’t all created equal. While it may seem straightforward that concrete mixes that contain lower density aggregates will weigh less than traditional concrete, the details of how a concrete mixture is produced can affect its strength and even its durability properties.
There are a few different types of concrete that fall into this category: Structural lightweight concrete, foamed concrete, and autoclaved aerated concrete (AAC). Structural lightweight concrete has an oven-dry weight below 800 kg/m3 and replaces dense natural aggregates with a combination of lightweight aggregates and air.
The most common aggregates for this type of concrete are pumice, tuff, scoria, and cinders. Pumice is spongy volcanic lava that has a pore structure and contains isolated voids; scoria is volcanic cinder that has tube-like, interconnected void pores. Tuff and cinders are volcanic rock byproducts that have low specific gravity.
These materials are often heat treated to enhance their ability to bind to the cement in a lightweight concrete mix and improve its strength. Adding crushed waste glass can also improve the mechanical properties of lightweight concrete.
Lightweight concrete solutions like SmartRock can make a significant difference in the time and cost of construction by reducing the amount of reinforcing steel required for floor slabs, especially in high-rise buildings. However, no matter which lightweight concrete mix a contractor chooses to use, it’s important that the concrete is tested for its strength in order to ensure it meets project specifications.
ASTM C494 specifies admixtures that affect the fresh properties of concrete. These include set accelerators and retarders, water reducers and superplasticizers. The use of these admixtures can help solve problems created by weather or site conditions.
For example, a temperature drop of 20o F can cut slump about 1”, increase concrete water requirements and lower the 28-day compressive strength by as much as 25%. To combat this, concrete producers can add an ASTM C494 Type A set accelerating admixture or a Type D combination of retarder and water reducer to the mix.
Chloride-containing set accelerators have been used in the past but are being replaced with non-chloride admixtures that meet ASTM C 494 Type B and can also act as an ASTM C 494, Type E, water reducer. These allow the concrete to be poured at higher temperatures for quicker placement, vibration or compaction without affecting initial or longer term strength.
High-range water reducers are referred to as superplasticizers and help to produce very thick concrete with little segregation. These admixtures typically meet ASTM C 1017 Types F and G and can be used with portland cement, fly ash, slag or silica fume to improve workability and strength.
foam generating equipment combines water with foam concentrate to produce finished fire fighting foam. The proportioning and application of the foam is essential to ensure proper fire extinguishment. The NFPA and EN standards specify the ratio of foam concentrate to water needed for an effective fire suppression. This ratio varies by type of fuel (hydrocarbons or polar solvent/alcohol) and is described as either 1 x 3 (1% water, 3% foam) or 1 x 5 (15% water, 5% foam).
The proportioning system typically utilizes an atmospheric storage tank with a positive displacement water motor powered pump. The pump is sized to accommodate the specific foam concentrate and can be operated on a variety of power sources including electric, diesel or gas engines.
In operation, the foam generator is controlled by a variable spray nozzle 2 which may be set to deliver a low, medium or high expansion foam. The nozzle is adjusted to direct the foam solution stream over the surface of a fixed or adjustable screen. As the solution comes into contact with the screen, it expands into millions of tiny stable bubbles that separate the fuel from oxygen, providing immediate fire extinguishment.
The DF130 mobile foam unit is designed and built for one man operation. It is an ideal solution for protecting oil and loading terminals, paint and solvent stores, boiler and engine rooms and diked flammable liquid storage areas. Delta also offers a full range of high expansion foam generators for use as part of a fixed installation.
Bricks are known for their durability and resistance to elements. However, they can be heavy and pose a danger for builders when lifting them during construction. Heavy lifting can cause low back pain or a herniated disc (a bulging of the disk material pressing on the spinal cord nerves that go to the legs). lightweight concrete bricks reduce this risk by reducing their weight. They can also help save money on installation costs because the wall can be constructed with fewer blocks.
The earliest versions of these blocks, commonly referred to in specifier terms as concrete masonry units or CMU, arrived on the scene over a century ago. These blocks are made with Portland cement and a lightweight aggregate, usually expanded shale. They are non-combustible and have good tensile and shear strength. However, their flexural tensile strength is less than that of conventional concrete.
Another advantage of these bricks is their ability to reduce heat transfer, which makes them a great option for areas with hot climates. Their insulating properties are also beneficial for colder zones. They are also very easy to apply paint to, which is a plus for anyone who wants their house to look attractive.
As a building material, these blocks are available in many different types. They are available as solid, fly ash, and cellular concrete bricks. Solid concrete bricks are usually used as load bearing and non-load bearing material in walls, partition walls, and panel walls. They are also used as backing for piers and retaining walls.
concrete release, whether in powder or liquid form, plays two roles on a stamped project: it prevents stamping mats from adhering to concrete and thereby disturbing the imprint texture, and it provides color accents that enhance the integral or dry-shake coloring system, creating an antiquing effect.
Powdered release agents, such as Walttools Powder Accent release, are applied just prior to stamping using a brush and flicked onto the concrete surface. They contain iron oxide pigments that not only act as a concrete releasing agent but provide a secondary tint for contrasting color in stamped or textured concrete.
Liquid releases, on the other hand, are sprayed on the concrete surface with a pump sprayer. Liquid release can also be tinted, but contractors have to add their own pigment a day or two before they plan to use it to make sure the color is well mixed and will dissolve properly.
When using tinted release, it's important to fog the stamp mats and concrete just ahead of where you are going to apply the product. If you don't, the release may evaporate before you get to that area and could contaminate the next color application with dark splotches or clumps of color.
Water-based emulsions are the latest product generation of concrete release and are used for reasons of health, safety at work and environmental hygiene, as they do not emit any toxic fumes during spraying. They are very easy to handle and, unlike products based on mineral oils, are fully compliant with the new regulations for immediate demolding of standard formwork. They are especially suitable for precast plants.
Do you want to transform your low-slump concrete that refuses to flow in forms? If so, you need a super plasticizer admixture. These admixtures are able to reduce water content in a concrete mixture and increase workability at the same time. They are a must for anyone who wants to use fly ash, slag, silica fume or other high-performance cements.
The difference between plasticizers and superplasticizers is that plasticizers are additives that increase the plasticity of a substance and they also act as dispersants to prevent particle segregation. Superplasticizers on the other hand, reduce the water requirement of a concrete mixture by making the particles of the cement and its hydration products negatively charged which causes an inter-particle repulsion and improves workability and mobility. They can even make concrete flow with a very low water-to-cement ratio and still produce a high compressive strength.
Another advantage of superplasticizers is that they do not affect the initial set. The only exception to this is a lignosulfonate-based superplasticizer which retards the set of concrete about an hour.
Fritz-Pak’s Super Slump Buster is a powdered viscosity modifying admixture (VMA) that helps with the problem of slump loss in concrete and provides superior workability, durability, corrosion resistance and water resistance. It can be added to any mix and is easy to use. Just sprinkle a small amount into the mix and mix for 2-5 minutes to see the results. Add more very gradually if necessary. It is important to remember that if too much VMA or superplasticizer is used, it will negatively impact the strength, set time and color of the concrete.
The concrete masonry units used in structures built with medium weight concrete (LC) have much higher compressive strengths than normal weight concrete, but they do not reach the same high levels as those of lightweight aggregate concrete or autoclaved aerated concrete. The increased strength is mainly due to the admixture of different types of air-entraining material in the mix.
The structural properties of LC are comparable to those of normal concrete (NC). In addition, it has good insulation characteristics. To satisfy the insulating requirements, the concrete must have a low bulk density. The concrete is therefore usually manufactured with different types of alternative aggregates. These may include more porous rock like pumice, industrial byproducts like fly ash or slag, or aerated natural raw materials such as clay, slate or shale that have been thermally expanded. The most common material is expanded clay from a single producer, which has a loose bulk density of up to 1120 kg/m3.
The quality of LC depends on the type of aggregates and the mixing process. Structural LC with coarse and fine aggregates made of standard NC is called conventional lightweight concrete (CLC) while CLC with only fine aggregates and no coarse aggregates is known as all-lightweight aggregate concrete or sand lightweight aggregate concrete (SLAC). For the sake of clarity, in this article we will refer to structural LC with an oven dry density between 1360 and 1920 kg/m3 and a minimum compressive strength of 17 MPa.
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Concrete is one of the most popular and widely used materials in construction today and there are a number of different types of additives or admixtures that can be added to make concrete a bit more interesting and more suitable for specific uses.
Generally the most common types of concrete mix additives are ones that are used to enhance the workability, durability or early strength of the concrete, but they can also be used to add colouring or even waterproofing to the mix too. These admixtures are usually liquid and can be added in very small amounts whilst mixing the concrete.
Water reducing admixtures are often used to help reduce the water content in concrete, this will cause a reduction in shrinkage. However this can lead to a loss of strength and may not be suitable for some applications, so it's important to know the differences between these types of admixtures before using them on your project.
Super plasticizer admixtures are another type of admixture that can be used to help increase the workability of your concrete. These admixtures are made up of chemical products that contain either formaldehyde derivatives or lignosulphonate compounds that reduce the water/cement ratio and can have many other benefits as well such as a reduction in shrinkage and increased strength.
Air releasing plastacizers are a fairly new type of admixture that can be added to your concrete, these plastacizers are basically foaming agents, they are able to introduce millions of tiny stable air bubbles into the concrete mix. This means that the concrete is much more workable and once cured it's extremely durable.
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