Silicate concrete: types, characteristics, production technology

Silicate concrete is a special kind of concrete with characteristics different from regular concrete. Silicate concrete, which is well-known for its strength and longevity, is utilized in many different types of construction projects that call for high-performance materials.

Making knowledgeable decisions during construction can be aided by having a thorough understanding of the various silicate concrete types and their unique qualities. Because of its exceptional qualities, which are a result of its composition and production process, this material is a popular choice in contemporary building practices.

This article will examine the different varieties of silicate concrete, their salient characteristics, and the manufacturing technology involved. By the time you’re done, you’ll know exactly why silicate concrete is a necessary component of the building industry.

General information and main characteristics of silicate concrete

The primary cementing ingredients of silicate concrete, an artificial building material, are chemical compounds of silica and calcium oxide hydrate that are either distributed as an additive or present in quartz sand.

Autoclave treatment significantly activates these components by guaranteeing the presence of liquid water at elevated temperatures (>100 °C) through high water vapor pressure.

The primary characteristic of silicate concretes is their fine-grained structure. Quartz-feldspar or conventional quartz sands can be used as fillers in these kinds of solutions.

The structure indicates that silicate autoclaved concretes can be:

  • dense heavy (filler – quartz sand):
  • dense light (porous filler of large or small fraction)
  • porous concrete (foam silicate or gas silicate).

Lightweight concrete based on siliceous components

Porous fillers, such as expanded clay, perlite, slag pumice, and other porous materials used as crushed stone or gravel, are the foundation of lightweight concrete. The same ingredients that are used to make dense, heavy concrete are also used as binders.

Three types of lightweight concretes are distinguished based on the density of the constituent materials and their architectural characteristics:

  1. Heat-insulating concrete (density up to 500 kg / m 3; thermal conductivity of the material – 0.18 W / (m- ° C)). They are used for thermal insulation of ceilings and roofs of public and industrial buildings.
  2. Structural and heat-insulating silicate concretes (material density: 500–1400 kg/m3; thermal conductivity of products — 0.58 W/(m-°C). They are used for the production of external enclosing concrete structures (wall panels, blocks, etc.).
  3. Structural lightweight concrete (product density 1400-1800 kg / m3) is used for the production of reinforced silicate concrete structures and precast concrete products.

Heavy concrete with silica aggregates

The two types of heavy concrete solutions are coarse-grained and fine-grained (sandy), depending on the size of the filler. The most prevalent in this category are fine-grained, sandy mixtures made of quartz sand and lime.

In contrast to regular cement, fine-grained heavy concretes on siliceous fillers have a more homogeneous structure because of a strong chemical bond between the filler grains and binders. Additionally, the cost of these concretes is a major selling point because it is significantly less than that of cement compositions with comparable grades.

The density of silicate heavy concretes ranges from 1800 to 2200 kg/m3. Tensile-compressive strength, which ranges from 100 to 600 kg/cm2, is contingent upon the mixture’s composition, fillers’ bulk densities, and the autoclave processing mode.

For instance, when laying the mixture by vibration, concretes on siliceous aggregates that have been autoclave treated and have a lime content of 8–11% of the total aggregate volume gain a strength of 100–300 kg/cm2. Furthermore, when 15–30% fine-grained quartz sand is added to the solution, and the mixture is properly compacted using the best autoclave heat treatment mode, the strength of the same material rises to 400–600 kg/cm^.

Porous lightweight concrete

Foam silicate and gas silicate are the two categories of materials from cellular (porous) concrete. A finely ground lime-siliceous mixture is combined with a special foam to create foam silicate, which is then processed through an autoclave to yield silicate products.

Combine aluminum powder with a lime-siliceous mixture to create gas silicate.

The most common are mixtures of gas silicates. However, there are instances where producing gas silicate products is far more profitable than producing comparable goods from aerated concrete.

The presence of a lime-siliceous binder in the aerated concrete solution’s composition enables you to qualitatively control the gasification process, which has a substantial impact on the density of the concrete’s cellular structure and, ultimately, the product’s strength.

Properties of silicate concrete

The indicators below illustrate the primary characteristics of silicate concrete:

  1. Water absorption of silicate products, depending on the method of compaction of the concrete mixture, is 10-18%.
  2. Frost resistance of high-strength silicate concrete reaches 100 cycles or more.
  3. High corrosion resistance – these parameters differ slightly from the indicators of cement concrete.
  4. Heat resistance.
  5. Resistance to temperature and atmospheric influences.
  6. Low cost of production of finished products.
  7. Durability (up to 70 years).

Materials for the production of silicate concrete

Finely ground quicklime, also known as slaked lime, is the primary binder in silicate concrete.Fillers round out the raw materials used in the creation of silicate concrete. A robust concrete product is created from the silicate concrete mixture by adding water and then heating it in autoclaves.

Lime used for the production of silicate mixtures must meet the following properties:

  • average hydration rate;
  • moderate exothermic effect;
  • the entire fraction must be equally burned;
  • MgO less than 5%;
  • lime slaking time — 20 minutes, no more.

The amount of material consumed increases when the lime mass is underburned. Overburning shortens the lime’s hydration period, which causes swelling, product surface cracks, etc.

When making silicate concrete, lime is typically used as finely ground lime mixtures with the following contents:

  • lime-siliceous — a combination of lime and quartz sand;
  • lime-slag (lime and blast furnace slag);
  • lime-ash — fuel shale or coal ash and lime;
  • lime-expanded clay and other similar components obtained from waste from industrial production of porous fillers;
  • lime-belite binders obtained by low-temperature firing of lime-siliceous dry mixture and quartz sand.

The following substances are applied as fillers for silica:

  • ground quartz sand;
  • metallurgical (blast furnace) slags;
  • thermal power plant ash.

Medium and fine fraction quartz sands are typically used as fillers; their composition should resemble this:

  • 80% or more silica;
  • less than 10% clay inclusions;
  • 0.5% or less mica impurities.

The strength and resistance to frost of silicate concrete are diminished when large clay inclusions are present in the quartz sand structure.

An important factor in the development of silicate concrete’s high performance qualities is finely ground quartz sand. As a result, silicate materials’ strength, resistance to frost, and other qualities improve as sand particle dispersion increases.

The following information is necessary when selecting components for the production of silicate concrete:

  1. Binder consumption increases proportionally to the increase in concrete strength.
  2. A decrease in the consumption of binders in the silicate mixture is observed with an increase in the dispersion of fine quartz sand, and increases with an increase in the molding moisture content of the silicate concrete mortar.
  3. The dispersion of ground quartz sand should be 2.5 times lower than the dispersion of ground lime.

Industrial production of silicate concretes

The conventional division of silicate concrete industrial production into multiple volumetric stages is as follows:

  • preparation of the necessary materials;
  • preparation of lime-siliceous mixture;
  • molding of silicate concrete products;
  • autoclave processing of silicate concrete.

The following independent departments are part of the company that produces silicate concrete products:

  • department for receiving materials for the manufacture of silicate concrete;
  • reinforcement department;
  • grinding shop;
  • concrete mixing department;
  • molding shop;
  • autoclave department;
  • warehouse of silicate concrete products.

The following is a rough technological instruction for producing silicate products in a factory setting:

  1. In the grinding shop, all the necessary components of lime-siliceous binders are crushed, sifted and dried. The components are ground in pipe or vibration mills.
  2. Then the materials, using a pneumatic pump, enter the concrete mixing department, where all the necessary components are dosed and loaded into a forced-action mixer. Water is added and mixed until a homogeneous mixture is obtained. To improve the mobility of concrete, aqueous solutions of plasticizers are added to its composition.
  3. The finished silicate concrete mixture is fed into the hopper of the concrete paver, with the help of which it is poured into prepared forms. The holding time before stripping the finished products must be at least 20 hours.
  4. After gaining the required strength, the products are stacked on trolleys and transported to the autoclave department for heat treatment using an electric transfer bridge.

Autoclave treatment of silicate products

The final and most crucial step in the creation of silicate concrete products is the autoclave treatment procedure. Thus, let’s examine the fundamental schematic of the autoclave operation to comprehend the core of the autoclave treatment procedure.

Autoclave device

Silicate concrete mixtures are transformed into silicate concrete products of a specific density with a range of shapes and uses through intricate processes that take place in the autoclave.

An autoclave for heat treatment is a cylindrical tank with hermetic spherical lids that is horizontally positioned and has an Ø of 2.6–3.6 m and a length of 20–40 m. The vessel has a safety valve that opens automatically when the pressure in the tank surpasses the critical value and a pressure gauge that measures the steam pressure.

At the bottom are rails for rolling trolleys filled with merchandise. Both the autoclave surface and the surface of the steam pipes are coated with a unique heat-insulating compound to minimize heat loss during heat treatment. The autoclaves also have mains for condensate discharge and bypass devices for moving used steam to the next autoclave.

General scheme of the process of autoclave processing of products

The ready autoclave is filled with molded sand-lime products, and the spherical lids are fastened securely. Saturated steam is then fed into the apparatus.

There are five main parts to the entire autoclave material processing process:

  1. Supply of wet steam with a temperature set in the autoclave equal to 100 ° C;
  2. Increase in steam pressure and increase in temperature to the technically necessary minimum.
  3. Thermal holding of products at the maximum permissible temperature and pressure.
  4. Gradually reducing the temperature to 100°C, and reducing the vapor pressure to atmospheric values.
  5. The process of cooling silicate products to 18–20°C can take place in an autoclave or in the open air.

The ability to effectively control the physical and chemical reactions that take place in autoclaves during different heat treatment stages determines the quality of autoclaved silicate concrete materials. The best method for quickening the strength gain of concrete products is autoclave heat treatment of the materials.

This chapter’s conclusion can be summarized as follows: making silicate products is a labor-intensive process that calls for specialized tools and specific knowledge. On a building site, silicate concrete can be prepared manually, but without autoclave treatment, it is nearly hard to get products of the necessary quality.

Consequently, it is best to buy silicate concrete and its products from specialized businesses that have staff members who have received training and specialized equipment. In this instance, you receive assurances regarding the building materials’ quality and the strength and durability of the structure that is built using them.

Type Characteristics and Production Technology
Autoclaved Silicate Concrete Made with lime, sand, and water. It’s cured in high-pressure steam (autoclaving), resulting in a durable and lightweight material. Used in blocks for walls and partitions.
Non-Autoclaved Silicate Concrete Also made with lime, sand, and water, but cured at normal pressure. It’s less strong than autoclaved types but easier to produce. Used in less demanding structural applications.
Foamed Silicate Concrete Incorporates foam agents to create a porous structure. Lightweight with good thermal insulation properties. Often used in insulating layers or lightweight blocks.

Silicate concrete is an exceptionally strong and adaptable material that can be used for a wide range of construction tasks. Because of its distinct qualities—like its high compressive strength and superior thermal insulation—builders seeking dependable performance find it to be a compelling option.

Making wise decisions during construction requires an understanding of the various types of silicate concrete and their intended applications. Whether used for insulation or structural components, each type has unique advantages that allow for application flexibility.

Silicate concrete is still a reasonably priced option for large-scale projects because of its simple and effective production technology. Because the method uses easily obtained materials, it is both sustainable and well-liked in the building sector.

Overall, silicate concrete offers a balance of strength, durability, and affordability, making it a valuable material for a wide range of construction needs.

A versatile building material, silicate concrete is renowned for its strength, resistance to fire, and ability to insulate sound. It is created by adding water to silicate-based materials, such as quartz sand and lime, and then autoclaving the mixture to cure it. There are various varieties of silicate concrete that are appropriate for different construction applications, such as insulation and load-bearing structures. Selecting the appropriate silicate concrete for a variety of construction projects is made easier by being aware of its properties and manufacturing process.

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Dmitry Sokolov

Chief engineer in a large construction company. I have extensive experience in managing construction projects and implementing modern technologies.

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