Binding Materials in Construction

• Binding materials conglutinate granular or bulk materials, acting as essential components in construction.
• Organic binding materials include asphalt, natural resin, and synthetic resin.
• Inorganic binding materials include air hardening and hydraulic binding materials.
• Air hardening binding materials include gypsum, lime, soluble glass and magnesia.
• Hydraulic binding materials includes Portland cement, aluminates cement and other kinds of cement.
• Binding materials are utilized in construction for making concretes and mortars.
• They are used in bonding together individual elements of structural components and in waterproofing.
• Mineral binding materials are subdivided into hydraulic, air-entrained, and acid-resistant types based on composition, properties, and use.
• Hydraulic binding materials preserve and increase strength in water after preliminary hardening in air.
• They are used in underground and underwater hydraulic-engineering along with Portland cement and its varieties.
• Air-entrained binding materials harden and maintain strength only in the air.
• They are used for aboveground structures not subject to water action - gypsum cements, magnesian cements, and air-hardening lime.
• Acid-resistant binding materials maintain their strength in air while in contact with acids.
• They're used in acid-resistant coverings, like acid-resistant cements made from water glass (sodium silicate).
• Organic binding materials are made of organic origin and can transition from a plastic state to hardness with physical/chemical processes.

Building Gypsum

• Gypsum consists mainly of calcium sulfate, having desirable characteristics for construction.
• Varieties include standard building gypsum, high-strength gypsum, anhydrite cement and high-temperature-calcined gypsum.
• Raw materials include natural dihydrate gypsum, anhydrite, and chemical by-products for producing gypsum cement materials.
• The gypsum used in construction is semi-hydrated gypsum.
• Gypsum production is through the processing of natural bihydrate gypsum, also known as calcined gypsum.
• Variation of heating methods and temperatures while processing will result in produced distinct varieties of gypsum.
• Gypsum is white, with a density of 2.6-2.75g/cm³, and a density of 800-1000kg/m³.
• Building gypsum is classified into high-class, first-class, and acceptable grades based on strength, fineness, and setting time.
• Water requirements for hydration require 18.6% of the weight of semi-hydrate gypsum.
• Water often accounts for 60%-80% to make the gypsum slurry have certain plasticity.
• Excess water evaporates during hardening, resulting in 50%-60% porosity, lower strength, low apparent density, low thermal conductivity and high sound absorption.
• The setting time changes with calcination temperature, grinding rate, and impurity content.
• Mixed with water, initial setting is a few minutes at room temperature, and final setting is within 30 minutes.
• Under dry indoor conditions, complete hardening needs about one week.
• Delayed can be added to reduce solubility and the solution rate of building gypsum
• Additives may be used to adjust the setting time; coagulants can delay, while accelerators can speed up the process.
• It expands a little during hardening, preventing cracks, and allowing it to be used alone without extenders for construction.
• Its porosity can reach 50%-60% after hardening, resulting in light, insulating, and sound-absorbing products.
• Large porosity results in a low strength and a high water absorption.
• Building gypsum has a low softening coefficient (about 0.2-0.3) and poor water resistance.
• Its main component is Calcium Sulfate Dihydrate after hardening, which releases crystal water when heated and provides very good thermal insulation.
• Fire resistance improves with product thickness.
• Has obvious plastic deformation, so it is less suited for load-bearing structures.
• Building gypsum, mixed with water and sand, turns into gypsum mortar for indoor plastering.
• Plastered walls will be insulating, fire-resistant, sound-absorbing, comfortable, and aesthetic.
• Plastered walls can be painted or pasted with wallpaper, and the gypsum mortar can be mixed with lime.
• When mixed with water and fiber-reinforced/plastic materials, gypsum can be used to create plaster sculptures and decorative panels because of its micro-expansion.
• Gypsum board is a wallboard with a gypsum plaster core bonded to layers of paper or fiberboard and used in interior walls.

Lime

• Lime is one of the earliest binding materials for buildings.
• The raw materials are abundant and widely distributed, the production process is simple and low-cost, and it is easy to use.
• The main raw material is natural rock which major component is calcium carbonate.
• Common lime materials include limestone, dolomite, and chalk with clay impurities controlled within 8%.
• Limestone generates quicklime after calcination, with a reactive mode CaCO3 ~ CaO+CO2.
• Calcination temperature is controlled within 1000-1100°C, based on heat loss, limestone density, block sizes, and impurities.
• Insufficient temperature and calcination generates under-burnt lime with less mortar yield and high temperature.
• Quicklime is white or grey with CaO as major component after calcination , the calcinated lime contains MgO correspondingly
• During aging, lime releases much heat, and expands 1-2.5 times in volume..
• Water demand involves 32.1% of lime's mass, because part of the water will evaporate, the water demand (60%-80%).
• The lime used in construction includes building quicklime, building quicklime powder, and building hydrated lime powder.
• The lime mortar generated by the aging of lime has good water retention.
• Carbonization of lime mortar in the air is slow, so the strength of hardened lime is low.
• A 1:3 lime mortar of 28 days has only 0.2-0.5 MPa strength.
• Calcium hydroxide is soluble in water and causes the hardened lime to scatter after a long time if immersed in water or exposed to moisture.
• Lime should not be applied in a humid environment.
• A large amount of water evaporates which will cause shrinkage of volume.
• Lime is mixed with fiber, paper pulp, and other shrinkage resisting materials..
• Lime powder can be made into silicate products when mixed with materials containing silicon.
• It can also be carbonized for the purpose of creating carbonized lime board.
• Mixed with a percentage of clay, lime can produce limestone soil or combined soil with addition of gravel and slag.
• Lime is stored as construction site, quicklime should not be exposed to moisture.
• The aging of lime will release a great amount of heat, so quicklime and inflammable matter should be stored separately to avoid fire.

Magnesia

• Magnesia is an air-hardening binding material whose major component is magnesium oxide (MgO).
• Its yellow or white powder material main material comes from natural magnesite, serpentine dolomite, molten slag from magnesium alloy smelting, or seawater.
• When magnesia slurry is made with water, setting and hardening are very slow and the strength after hardening is low.
• It is common to add modifier to accelerate the hardening process.
• Magnesium chloride solution will lead to faster setting and hardening and improved the strength.
• Magnesia is divided into high-class grade (A), first-class grade (B), and acceptable grade (C) based on chemical and physical properties.
• Magnesia and plant fibers bind strongly, avoiding decomposition of fibers.
• Magnesia is mixed with wood chips and fibers to produce xylolite floor, wood-cement board, and xylolite slab.
• Fillers like French chalk and brick powder are added to improve wear resistance.
• Magnesia board is high tightness and intensity, has sound absorption, and thermal insulation.
• Reinforced magnesia has a high intensity and can be used instead of wood.
• Adding a foaming agent can make magnesia into light and porous thermal-insulating material.
• The water resistance of magnesia is poor, and its products should not be stored in humid places.
• These products should not be used with steel bars due to the chloride ions from the chloride solution used during its production.

Soluble Glass

• Soluble glass, also called foam alkali, is an alkali metal air-hardening material.
• It is used to prepare sodium silicate cement, soluble glass mortar, and soluble glass concrete.
• It is used in anti-acid and heat-resistant engineering.
• Soluble glass is produced by grinding and stirring calcined soda and quartz sand, then fusing them in the melting pot of 130O-140OoC.
• Liquid soluble glass is obtained by dissolving solidified soluble glass by steaming or heating quartz sand/sodium hydroxide.
• Pure soluble glass solution is colorless, but often appears steel grey or yellow-green due to impurities.
• Absorbing carbon dioxide in the air will generates amorphous silicate and gradually becomes dry until hardening.
• To quicken the hardening, soluble glass is often heated or mixed with sodium fluosilicate as an accelerator when using.
• The appropriate amount of sodium fluosilicate should account for 12%-15% of the.
• The solid soluble glass with low module is relatively easy to dissolve in water.
• If urea is added into soluble glass, its cohesive force can be improved without modifying the viscosity.
• It can resist the majority of inorganic acids, organic acids, and corrosive gases.
• Silicate gel blocks the capillary porosity of the material to prevent water infiltration.
• Also good heat resistance, so it does not dissolve and its strength does not decrease and is even increased by high temperatures.
• Can be used as binding material for acid-proof plaster, acid-proof mortar, and acid-proof concrete in anti-acid projects.
• It is made into heat-resistant concrete and mortar.
• Soluble glass solution can be used to paint building materials or porous materials.
• Soluble glass solution and calcium chloride solution are injected resulting with a cement reaction with prevent infiltration.
• Can be used as water-proof agent for cement by using alum solutions.