Technical characteristics and application progress of lightweight aggregate concrete

1. Introduction

Lightweight aggregate concrete is a type of concrete made of lightweight aggregate (with a density less than1800kg/m³The porous aggregate is a new type of concrete material prepared by mixing coarse aggregate with cementitious materials, additives, and water. Compared with ordinary concrete, its significant advantages lie inLightweight, insulated, and soundproofAt the same time, it has good durability and processability, which is in line with the current construction industry“Energy saving, environmentally friendly, and high-performance”The development needs have become structural and functional materials in modern construction engineering.

2、 Material composition and function

The performance of lightweight aggregate concrete depends on the synergistic effect of each component, and the main constituent materials and functions are as follows:

1. lightweight aggregate

Lightweight aggregate is the core component that determines the lightweight properties of concrete. According to the source, it can be divided intoNatural lightweight aggregate(such as pumice, volcanic slag, tuff) andArtificial lightweight aggregate(such as ceramic particles, fly ash ceramic particles). among which,ceramsiteEspecially shale ceramic particles and fly ash ceramic particles, due to theirClosed pore structure, low water absorption, high strengthThe compressive strength can reach5-30MPa）Becoming lightweight aggregate concrete for structural use; Vermiculite and other materials have extremely low density（<300kg/m³）It is commonly used for thermal insulation layers.

2. cementitious material

Mainly composed of cement (Portland cement, ordinary Portland cement), with the addition of admixtures such as fly ash, slag powder, and silica fume. The functions of admixtures include:（1）Replace some cement to reduce costs and carbon emissions; （2）Improve the workability of fresh concrete (such as the ball rolling effect of fly ash); （3）Improve the durability of hardened concrete (such as filling pores with volcanic ash reaction of slag powder).

3. admixture

Key additives includeEfficient water reducing agent(such as polycarboxylic acid series)air-entraining agentandwater-retaining agentEfficient water reducing agents can significantly reduce the water cement ratio (from0.5-0.6drop to0.3-0.4）Improve the strength and compactness of concrete; Air entraining agent can introduce tiny enclosed bubbles to improve frost resistance (frost resistance level can reach)F100-F200）； Water retaining agents (such as hydroxypropyl methyl cellulose) are used to suppress excessive water absorption of lightweight aggregates and prevent loss of slump in fresh concrete.

4. water

The water consumption needs to be strictly controlled to meet the hydration requirements of the cementitious material while avoiding the floating of lightweight aggregates due to excessive water (lightweight aggregates have low density and are prone to separation during mixing). usually adopted“Pre wetted lightweight aggregate”Process (soaking lightweight aggregate)2-4After drying the surface, use it to reduce its absorption of mixing water.

3、 Main performance characteristics

1. Lightweight characteristics

The dry density of lightweight aggregate concrete is generally1400-1900kg/m³Ordinary concrete is2400kg/m³Left and right), the weight can be reduced20%-50%This characteristic can significantly reduce structural loads (such as using lightweight aggregate concrete for high-rise residential walls, which can lower the foundation bearing capacity requirements)15%-25%）Reduce the cost of basic engineering while improving the seismic performance of buildings (seismic action is proportional to the weight of the structure).

2. Thermal insulation performance

The porous structure of lightweight aggregate gives it a low thermal conductivity（0.5-1.5W/Ordinary concrete is1.8-2.0W/）. For example,200mmThe insulation effect of thick ceramic aggregate concrete walls is equivalent to400mmThick ordinary brick walls can significantly reduce the energy consumption of building heating and cooling (with an energy-saving rate of up to30%-50%）, in accordance with“Passive room”“Zero energy buildings”The requirements.

3. Sound insulation performance

The pore structure of lightweight aggregate can effectively absorb sound waves, and its airborne sound insulation can reach up to45-55dBOrdinary concrete is35-40dB）. When used for partition walls or floor slabs, it can significantly improve the indoor acoustic environment and meet the sound insulation requirements of residential, hotel and other places.

4. durability

（1）Impermeability: Lightweight aggregates with closed pores such as ceramic particles can reduce the capillary channels inside concrete, and the impermeability level can reachP6-P10Ordinary concrete isP4-P8）；

（2）Frost resistance: The tiny bubbles introduced by the air entraining agent can alleviate the damage of freeze-thaw cycles to concrete, and the frost resistance level can reachF100-F200(Applicable to projects in cold regions);

（3）Carbonization resistance: Low water cement ratio and dense structure can delay the carbonation process, and the carbonation depth is lower than that of ordinary concrete30%-50%.

4、 Key points of preparation process

1. Mix Proportion Design

（1）Determine density grade: Choose according to the purpose, for example, the density grade of lightweight aggregate concrete used in structures is1600-1900kg/m³For insulation purposes1400-1600kg/m³；

（2）Strength design: by adjusting the dosage of cementitious materials（300-500kg/m³）Compared to water cement ratio（0.3-0.45）Control strength, the strength grade of lightweight aggregate concrete for structural use can reachC20-C40；

（3）Adjustment of workability: By pre wetting lightweight aggregates, adding water reducing agents and water retaining agents, the slump of fresh concrete is ensured to be within100-150mm(Requirements for pumping construction).

2. Mixing process

（1）Pre wetted lightweight aggregate: Soak the lightweight aggregate in a saturated surface dry state (with no free water on the surface) to avoid absorbing mixing water during mixing;

（2）Mixing sequence: Mix the lightweight aggregate with some water first1-2Minutes, then add cement, admixtures, and additives and stir2-3Minutes, and finally adjust the water consumption to mix evenly (the total mixing time shall not exceed5Minutes);

（3）Prevent separation: Avoid excessive vibration during the mixing process to prevent light aggregates from floating and causing layering.

3. Pouring and maintenance

（1）Pouring: Adopt layered pouring (each layer thickness not exceeding300mm）The vibration is carried out using a flat vibrator or an insertion vibrator (with a shorter vibration time than ordinary concrete)30%）；

（2）Maintenance: After pouring12Cover with moisturizing agents (such as plastic film, burlap bags) within hours and spray water for maintenance7-14Tian (lightweight aggregate has strong water absorption and needs to prevent surface cracking due to water loss).

5、 Application Fields

1. residential building

High rise residential buildingswall(such as shear walls, infill walls)floor slabUsing lightweight aggregate concrete (such as composite panels) can reduce the self weight of the structure (reducing the self weight of the wall per square meter)50-100kg）Increase the building plot ratio (increase)1-2Layer). For example, in high-rise residential projects in cities such as Beijing and Shanghai, the proportion of ceramic aggregate concrete walls has reached60%The above.

2. industrial building

factory buildingroof panel、crane beamUsing lightweight aggregate concrete can reduce roof load (decrease in self weight per square meter of roof)80-120kg）Increase the span (from6-8mIncrease to10-12m）. For example, in the joint factory building of an automobile manufacturing plant, the application rate of lightweight aggregate concrete roof panels reaches80%.

3. energy-efficient building

Passive houses and zero energy buildingsExternal wall insulation layerUsing lightweight aggregate concrete for external insulation composite walls can meet the requirements“External wall heat transfer coefficient≤0.15W/”The requirements. For example, in a passive housing project in Berlin, Germany,250mmThe thick fly ash ceramic aggregate concrete exterior wall achieves the goal of not requiring heating in winter.

4. Municipal Engineering

bridge'sbridge deck pavement、pierBy using lightweight aggregate concrete, the bridge load can be reduced (reducing the self weight of the bridge deck per square meter)100-150kg）Extend the service life of bridges (reduce fatigue damage). For example, the pavement layer of the Hangzhou Bay Cross Sea Bridge uses ceramic aggregate concrete, which reduces the overall load of the bridge.

6、 Development Trends

1. 高性能化

developmentHigh strength lightweight aggregate concrete(Strength level)≥C50）Used for load-bearing components such as columns and beams in super high-rise buildings, meeting the needs of large spans and high loads. For example, in a super tall building in Houston, USA,C60The application of ceramic aggregate concrete columns has reduced the column cross-section (from1.2m×1.2mdrop to0.8m×0.8m）.

2. greening

利用industrial waste residuePrepare lightweight aggregates (such as fly ash, slag, and steel slag) to replace natural aggregates (reduce mining) and lower cement usage (with a substitution rate of up to)30%-50%）. For example, the annual production of fly ash in China is about5One billion tons, of which10%Used for producing lightweight aggregate concrete, reducing carbon emissions by approximately1Billions of tons.

3. functionalization

developmentFireproof lightweight aggregate concrete(Adding fire-resistant fibers, fire resistance limit)≥3Hours)Soundproofing lightweight aggregate concrete(Adding sound insulation materials, air sound insulation capacity)≥60dB）TheSelf insulating lightweight aggregate concreteComposite insulation layer, heat transfer coefficient≤0.1W/）Meet the special needs of different places.

4. standardization

Develop a comprehensive planStandard for lightweight aggregate concrete(such as the Technical Specification for Lightweight Aggregate Concrete)JGJ 51-2019）Standardize material performance, mix design, construction technology, and other aspects to improve project quality (reduce problems such as cracks and substandard strength caused by improper construction).

VII. Conclusion

Lightweight aggregate concrete as a typeLightweight, energy-saving, and environmentally friendlyThe new materials have broad application prospects in the construction industry. With the continuous development of high-performance, green, and functional technologies, lightweight aggregate concrete will further replace ordinary concrete and become the mainstream material for future construction projects. In the future, it is necessary to strengthen the research and development of lightweight aggregates (such as nano modified lightweight aggregates) and optimize the preparation process (such as...)3DPrinting lightweight aggregate concrete, promoting the industrial application of lightweight aggregate concrete, and providing support for the sustainable development of the construction industry.