HPMC Dosage Guide for High-Performance Concrete

High-Performance Concrete is widely used in modern construction projects due to its high strength, durability and good construction performance. Hydroxypropyl methylcellulose (HPMC), as an important admixture, can improve the construction performance of concrete, increase water retention and optimize workability.

1. The role of HPMC in high-performance concrete

HPMC is a water-soluble polymer that plays the following main roles in concrete:

Enhance water retention: reduce water evaporation, increase cement hydration, and prevent early cracking of concrete.

Improve construction performance: enhance the viscosity of concrete, prevent segregation, and improve pumping and construction performance.

Improve durability: reduce porosity, improve impermeability and frost resistance, and make the concrete structure more stable.

Delay setting time: In high temperature environments, it helps to delay the setting time of cement and ensure the controllability of construction operations.

2. Recommended dosage of HPMC

The dosage of HPMC in high-performance concrete is affected by many factors, such as cement type, aggregate properties, ambient temperature and construction requirements. Generally speaking, the dosage is recommended as follows:

Conventional dosage range: The dosage of HPMC is usually 0.01%~0.05% of the cement mass, that is, about 0.1~0.5 kg of HPMC is added per ton of cement.

Low-strength high-performance concrete (C30-C40): The recommended dosage is 0.015%~0.03% of the cement mass to maintain good fluidity and water retention.

Medium-strength high-performance concrete (C40-C60): The recommended dosage is 0.02%~0.04% to optimize adhesion and durability.

High-strength high-performance concrete (C60 and above): The recommended dosage is between 0.03%~0.05% to ensure good crack resistance and adhesion.

3. Factors affecting the dosage of HPMC

The optimal dosage of HPMC needs to be adjusted according to the specific construction conditions. The main influencing factors include:

Water-binder ratio: A lower water-binder ratio (W/B < 0.4) requires a higher dosage of HPMC to prevent the concrete from being too low in viscosity, segregating or bleeding.

Ambient temperature: Under high temperature, water evaporation is accelerated, and the dosage of HPMC can be appropriately increased to improve the water retention effect.

Additive compounding: HPMC may produce synergy or mutual influence with admixtures such as water reducers and air entraining agents. The optimal ratio should be determined through experiments.

Construction method: Pumped concrete requires a higher viscosity, and the dosage of HPMC can be appropriately increased to improve pumpability and fluidity.

4. HPMC addition method

The method of HPMC addition can affect its dispersibility and effect. It is recommended to follow the following method:

Dry addition: HPMC can be premixed with cement, fly ash and other powders and added to the mixer to ensure uniform distribution.

Wet addition: HPMC can be dissolved in water to form a colloidal solution before adding it to the concrete mixture to ensure better uniformity and effectiveness.

The reasonable amount of HPMC in high-performance concrete is crucial to optimize construction performance, improve durability and reduce cracks. The generally recommended dosage is between 0.01% and 0.05% of the cement mass, and should be adjusted in accordance with specific project requirements and environmental conditions. By properly selecting HPMC, the comprehensive performance of concrete can be effectively improved, providing a better solution for engineering construction.