Application of novel admixtures in concrete brick making: strength enhancement and performance optimization

Abstract: The efficiency and product quality of concrete brick machine production largely depend on the application level of admixture technology. This article focuses on the core role of novel admixtures in concrete brick machine production, exploring it from two dimensions: strength enhancement and performance optimization. Combining the latest research and practice, the article analyzes the mechanisms of action and application effects of polycarboxylate superplasticizers, chemical accelerators, nano-modified materials, and composite admixture systems, aiming to provide a reference for brick machine manufacturers to upgrade their products through material innovation.

I. Introduction: New Requirements for Admixtures in Brick Machine Production

Concrete bricks (including blocks, paving bricks, permeable bricks, etc.) are important wall and paving materials, and their mechanical properties and durability directly affect the quality of construction projects. The brick machine molding process places special requirements on concrete mixtures: molding and demolding must be completed in a short time, and the products must have early strength to support turnover while meeting long-term durability indicators. Against this backdrop, traditional admixtures are no longer sufficient to meet multiple performance requirements, making the development and application of novel admixtures a focus of industry attention.

II. Core Path to Strength Enhancement: From Water Reduction to Activity Activation

1. Polycarboxylate Superplasticizer: High Water Reduction Rate Lays the Foundation for Strength

Water reduction is the primary means of improving concrete strength. At the same water-cement ratio, a higher water reduction rate results in more complete cement hydration, naturally increasing density and strength. New polycarboxylate superplasticizers, with their designable molecular structure, have become a core admixture type in brick-making production.

Molecular Design and Performance Matching: Through specific design of the structure, acid-ether ratio, and molecular weight of polycarboxylate superplasticizers, they can be better matched with the cementitious material system used in brick-making (such as composite cement mixed with fly ash and slag powder), promoting cement hydration speed and effectively improving early strength.

Nanomaterial Composite Modification: Introducing nanomaterials into the polycarboxylate superplasticizer system is a significant breakthrough in recent years. For example, polycarboxylate superplasticizers containing nano-silica can not only exert a highly efficient water reduction effect but also utilize the nucleation effect of nanoparticles to accelerate hydration while filling micropores, achieving multiple effects of "water reduction + strengthening + density". Studies show that optimized water-reducing agent compositions can significantly improve the compressive strength of concrete by regulating the hydration process and optimizing the pore structure.

2. Chemical Accelerators: Overcoming the Early Strength Bottleneck

Brick machine production has a rigid requirement for demolding strength. Traditional chloride-based early strength agents may pose a risk of steel reinforcement corrosion, while novel chloride-free accelerators have become a research hotspot.

Application Research of Magnesium Chloride (MgCl₂) Accelerator: A study on slag powder (GGBS) composite concrete showed that when MgCl₂ was added at a 10% dosage as a chemical accelerator, the 28-day compressive strength reached 51.28 MPa, significantly better than the blank control group. The mechanism lies in the fact that MgCl₂ promotes the early hydration reaction and achieves local microstructural densification and pore structure optimization. This approach has important reference value for brick machine concrete containing a large amount of industrial waste.

III. Multidimensional Expansion of Performance Optimization: Beyond Strength

Modern brick machine products not only require high strength but also need to consider durability, workability, and special functions (such as permeability and heat insulation). Novel admixtures achieve systematic performance optimization through multiple mechanisms.

1. Microstructure Control: From "Thicker" to "Denser" The performance of concrete ultimately depends on its microstructure. Novel admixtures focus on optimizing the interfacial transition zone (ITZ) and pore structure.

Shrinkage-Reducing and Modified Polycarboxylate Superplasticizers: By introducing shrinkage-reducing functional groups, drying shrinkage can be reduced without compromising strength, thus lowering the risk of cracking.

Nano-Reinforced Admixtures: Composite admixtures made of alkenyl-modified silane chitosan and other nanomaterials can reduce the chloride ion diffusion coefficient, improve the impermeability and density of concrete, thereby enhancing durability.

2. Multi-Component Synergy: Advantages of Composite Admixture Systems Single admixtures are insufficient to meet all performance requirements; composite admixtures are an inevitable trend.

"Cost Reduction and Efficiency Enhancement" of Admixtures: New concrete admixtures can significantly improve the cohesiveness and pumpability of concrete, and while maintaining the same strength grade, can reduce cement usage by approximately 10%–15%, directly reducing the raw material costs of brick machine production.

Functional Component Compounding: In the preparation of energy-saving and environmentally friendly bricks, the formula often includes water-reducing agents, retarders, air-entraining agents, and antifreeze agents. For example, rosin resin-based air-entraining agents can improve the durability and rheological properties of concrete; molasses retarders can regulate setting time, ensuring smooth connection between the brick machine's mixing and molding processes.

3. Exploration of Novel Bio-based and Nano-admixtures: To meet the needs of sustainable development, researchers are exploring the use of renewable resources to prepare admixtures.

Nano-reinforced bio-additives: Cellulose nanocrystals (CNCs), derived from plant waste, can significantly improve strength and reduce porosity through nucleation and pore refinement effects when added in small amounts (0.1-2 wt%). Chitosan (derived from crustacean waste) possesses film-forming and ion-complexing capabilities, reducing permeability and endowing materials with certain self-healing potential.

IV. Application Practice and Prospect in Brick Machine Production

In actual brick machine production, the selection and dosage of admixtures need to be adapted to the specific brick type, raw material quality, and molding process.

Optimization for industrial waste bricks: For brick machine production lines that heavily utilize fly ash, slag, and construction waste, chemical accelerators or nanocrystalline nucleus-type admixtures can be introduced to compensate for early strength loss due to reduced cement usage.

Adaptation for functional bricks: When producing permeable bricks, a balance between strength and permeability is required; the admixture scheme must consider both water retention and reinforcement. When producing thermal insulation blocks, air-entraining agents and reinforcing agents can be combined to achieve lightweight and high strength. Conclusion: The application of novel admixture technology in concrete brick making has evolved from a simple "water reduction and enhancement" approach to a deeper optimization stage characterized by "multi-element synergy, micro-control, and functional integration." By scientifically selecting polycarboxylate superplasticizers, chemical accelerators, nano-modified materials, and composite functional components, brick making manufacturers can not only effectively improve product strength but also achieve significant benefits in cost reduction, durability improvement, and solid waste utilization. In the future, with the maturation of bio-based materials and intelligent responsive admixtures, brick making is expected to usher in a new round of technological upgrades.