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The application of CSA cement in dry mixed mortar products

Ultra High Strength CSA Cement (HCSA) is the high performance cement based on high strength CSA cement, which improves the quality of raw materials, strictly controls the production process, and does not add any mixed materials.  Since the cement is mainly composed of 3CaO·3Al2O3·CaSO and 2CaO·SiO2, the main hydration product of the reaction, ettringite (3CaO·Al2O3·3CaSO4·32H2O), making it has the advantages of early fast setting, fast hardening and micro-expansion.  It has good compatibility with Portland cement compounding and improves the comprehensive physical properties.  Compared with aluminate cement, its strength development is stable, it does not shrink in the later stage, and the cost performance is higher, which is more suitable for dry-mixed mortar products.

1. Classification of ultra high strength CSA cement

Ultra high strength CSA cement can be divided into: CSA92.5, CSA82.5 and CSA72.5; according to its type, it can be divided into: type I, type II and type III.

2. Technical indicators of ultra high strength CSA cement

The specific surface area is divided into two types: 360m2/kg~430m2/kg (standard requirements>360m2/kg); 450m2/kg~500m2/kg (standard requirement>450m2/kg).  Setting time: initial setting > 10 minutes, final setting <350 minutes.

3. Performance characteristics of ultra-high strength CSA cement

Common points of CSA cement:

(1) Short condensing time, high early strength, and early solidification and fast hardness.  The main mineral composition is C4A3S and C2S, and the special mineral composition gives the material special properties.

(2) High density and excellent corrosion resistance.
Since the mineral component does not contain 3CaO·Al2O3 (C3A for short), the Ca(OH)2 content in the cement stone is extremely low, so it is resistant to soft water and sulfate attack. The main hydration product is dense 3CaO·Al2O3·3CaSO4·32H2O (abbreviated as ettringite), which greatly reduces the void ratio of cement stone and improves the impermeability and corrosion resistance.

(3) Good anti-freezing performance, after adding special anti-freezing agent, it can be used for concrete construction in winter -30 °C state.

(4) The liquid phase PH is low, and no alkali aggregate reaction occurs, especially the alkali-carbonate reaction effect is excellent.

(5) The strength development is stable, and the strength does not shrink in the later stage. The CSA cement introduces gypsum during the clinker firing process, which acts as a guiding compound and stabilizes the minerals, improves the activity of the clinker and ensures a good crystal form transformation, and later introduces the gypsum with the architectural high alumina cement.  There is a fundamental difference in the formation of ettringite.

Matching with Portland cement:

(1) Adjust the setting time and increase the early strength. The main hydrated minerals of ultra high strength CSA cement are C4A3S and C2S. Ca(OH)2 precipitated by CaSO4 and C3S in Portland cement can accelerate the coagulation of C4A3S and rapidly form ettringite. When CaSO4 is consumed by C4A3S in Portland cement, it is not enough to achieve the desired retardation. At the same time, as Ca(OH)2 is removed, the hydration of C2S is accelerated. Therefore, the surface of these two cement particles  The hydration products interact violently, greatly speeding up the hydration rate and shortening the setting time.

(2) Increase the surface compactness. Under the joint action of C-S-H produced by Portland cement hydration and 3CaO·Al2O3·3CaSO4·32H2O produced by hydration of ultra high strength CSA cement, the void ratio of cement stone is greatly reduced, the compactness is increased, and the mechanical strength is improved.

(3) Reduce shrinkage and prevent cracking. In the Portland cement ultra high strength CSA cement-gypsum ternary system, it can effectively reduce the shrinkage after plastic shrinkage and hardening, and solve the large shrinkage caused by the excessive water-cement ratio of the fluid mortar. Avoid cracking.

(4) Improve rheological properties.  Practice has proved that in the Portland cement ultra high strength CSA cement-gypsum ternary system, ultra-high-strength CSA cement can increase the fluidity and improve the rheology within a certain range.

Practical application of ultra-high strength CSA cement in dry mortar

4. The application of CSA cement in dry mixed mortar products

I. Application in cement self-leveling mortar

Ultra high strength CSA cement can play a good role in cement self-leveling mortar:
(1)To increase surface mechanical strength;
(2) increase early strength;
(3) reduce shrinkage and control cracking;
(4) increase surface decorative effect, good tinting strength;
(5) Improve fluidity at a certain dosage.

In the Portland cement-ultra-high-strength CSA cement-gypsum ternary system, whether it is Portland cement or ultra-high-strength CSA cement, as long as the ratio is appropriate, it can be formulated with excellent performance self-leveling mortar.  In contrast, self-leveling mortar based on Portland cement has a longer setting time, generally initial setting in 70 minutes to 120 minutes, suitable for preparing thicker self-leveling mortar to ensure sufficient working time and Good liquidity. The self-leveling mortar with super high-strength CSA cement has a short setting time, and it can be solidified and hardened in 30 minutes to 60 minutes. It is very suitable for thin-layer self-leveling and engineering with high early strength requirements.  At the same time, in the ternary system, ultra-high-strength CSA cement plays a key role in reducing the dimensional change rate, and the dimensional change value can reach ±0.05%, which is better than JC/T985-2005 “cement-based cement-based self-leveling mortar”.  The dimensional change value required in the article is ±0.15%.  In the process of actual application, it was found that due to the limitations of the site conditions, many ground bases did not have a waterproof layer, and some sidewalls were leaky. Some projects were retrofitted with old houses, and the base water was large, far exceeding the humidity requirement.  In such cases, a shorter expansion stability period is especially important for self-leveling mortars, and the addition of ultra-high-strength CSA cement has successfully solved this problem.

The appearance of ultra-high-strength CSA cement is yellow-white, which improves the color of the material in the ternary system (especially based on ultra-high-strength CSA cement) and has a good decorative effect, especially in the preparation of colored cement self-leveling mortar.  The effect is better.

II. Application in non-shrinkage grouting materials

Ultra-high-strength CSA cement can play a good role in non-shrinkage grouting materials:
(1) increase early strength, and the strength continues to grow steadily;
(2) compensate for shrinkage and effectively prevent cracking;
(3) use alone, Formulating special grouting materials with high hour strength;
(4) enabling grouting materials to achieve winter construction.

Ultra-high-strength CSA cement is added to the ternary system based on Portland cement, which can compensate for the later shrinkage and improve the early strength.  The ternary system based on ultra-high-strength CSA cement can still prepare grouting materials with high hour strength (2 hours compressive strength greater than 30 MPa) while ensuring high fluidity and sufficient working time. In addition to being added to ordinary non-shrinkage grouting materials in the form of mineral additives, ultra-high-strength CSA cement can also be used as a grouting material for high-speed railway passenger line basin rubber in combination with gypsum and admixture.  Used in projects those require high hour strength.  Special grouting materials formulated with ultra-high strength CSA cement can be used for winter construction at a minimum temperature of -30 °C.  Since the material itself has micro-expansion, after adding the plastic expansion component, the plastic state and the "double expansion" function after hardening are achieved, and the maximum vertical expansion rate of 3 hours can reach 3.5% (3 hours and 24 hours of expansion).  The difference between the values is less than 0.02%).

III. Application in tile adhesives and grouts

Ultra-high-strength CSA cement has early-hardening and fast-hardening properties, and can be formulated into fast-hardly tile adhesives.  Adding to the grouting agent can compensate for shrinkage and effectively prevent alkali return.  Because C2S and C3S in Portland cement also produce a large amount of Ca(OH)2 in the formation of hydrated CSH, it is a highly deliquescent substance that migrates to the mortar surface and air as the water evaporates.  The action of CO2 in the process produces CaCO3 and returns to the base.  After the introduction of ultra-high-strength CSA cement, 3CaO·3Al2O3·CaSO4 generates ettringite Aft swelled crystals in the pores of the pores under the excitation of Ca(OH)2 and CaSO4, preventing the free water from oozing out.  It plays a role in inhibiting the return of alkali.

IV. Application in exterior wall thermal insulation mortar

Ultra-high-strength CSA cement is used in exterior wall thermal insulation mortar:
(1) It can quickly harden the bonded mortar after boarding, improve construction speed and shorten the construction period;
(2) It can improve the surface hardness and compactness of the plastering mortar;
(3) The material can be used normally at lower temperatures.

Ultra-high-strength CSA cement can achieve rapid solidification under the premise of satisfying the sufficient working time of the bonded mortar. Ultra-high-strength CSA cement has excellent adhesion to EPS/XPS sheets, and the bonding strength that other bonding materials take 28 days can be achieved in one day.  This not only enables rapid construction (the next step of smoothing mortar construction can be carried out after 4 hours at room temperature), but also reduces the amount of polymer used in the mortar and reduces the material cost.  The introduction of ultra-high-strength CSA cement, combined with high-molecular polymer and early strength agent, can make the minimum use temperature of plastering mortar reach -7 °C (other common materials are 0 °C), the mortar will not be frozen and  Has good adhesion.

V. Application in plugging materials

Ultra-high-strength CSA cement is applied to the plugging material, which makes the setting time short, the hardening speed is fast, and the long-term stability is good.  Under normal circumstances, the use of ordinary cement composite quick-setting admixture or composite cement system to prepare the plugging material, although it is a shorter setting time, rapid hardening can not achieve, that is, "speed coagulation is not early strong", and It is difficult to meet the requirements of use in the actual application process.  The plugging material prepared with ultra-high-strength CSA cement can be arbitrarily adjusted within ten seconds to several minutes, and once it is hardened by condensation, the purpose of "fast setting and fast hardening" is realized. Plugging products often prolong the setting time due to the long storage time (generally the shelf life is 6 months), thus seriously affecting the use effect. The plugging material mainly prepared by ultra-high-strength CSA cement (referred to as ultra-high-strength csa cement plugging material) mainly relies on accelerating the hydration reaction between minerals to achieve the effect of quick setting, which is completely different from ordinary plugging.  The hydration and condensation method of the leakage material, such as Portland cement plus a variety of quick-setting agents (referred to as Portland cement plugging materials), and Portland cement mixed special cement added a variety of quick-setting agents (referred to as composite cement plugging) .Material), ultra-high-strength CSA cement plugging material does not produce the "adsorption" and "reaction" of the admixture, and has good storage and long-term stability.  Take the above three kinds of samples of plugging materials, then adjust to have the same setting time (2 minutes of initial setting, 3 minutes of final setting), and compare the test. The order of early strength development from fast to slow is: super high-strength sulphuric acid .Salt cement plugging material> Portland cement plugging material> Composite cement plugging material.

As a key component of dry-mixed mortar products, ultra-high-strength CSA cement is dry-mixed since its launch on the market due to its unique properties of early strength, fastness, corrosion resistance, micro-expansion and frost resistance.  The mortar industry is favored by people, and is widely used in cement self-leveling mortar, non-shrinkage grouting material, tile adhesive and grouting agent, exterior insulation system materials, waterproof plugging materials, quick repair materials, etc.  The comprehensive performance of the product has been well received in the actual application process.
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