Differences in cement varieties

• Ordinary Portland cement has high activity of mineral components, with the initial setting time usually controlled within 45 minutes and the final setting time not exceeding 10 hours, which is suitable for conventional construction scenarios.
• For admixture cements such as slag Portland cement and pozzolanic Portland cement, due to the long cycle of the secondary hydration reaction, their final setting time can be extended to 12-15 hours.
• The type of cement should be selected according to the project progress requirements.

Water-cement ratio balance control

• When the water-cement ratio exceeds 0.6, excess water forms capillary pores during the hardening stage, which not only prolongs the final setting time but also reduces the 28-day compressive strength by 15%-20%.
• If the water-cement ratio is lower than 0.4, the slump of the concrete mixture is insufficient, which can easily lead to poor vibration and hinder the local hydration reaction.
• In actual projects, the water-cement ratio of pumped concrete is mostly controlled in the range of 0.45-0.55, and water reducers are used to optimize working performance.

Dynamic response of ambient temperature

• Experimental data show that for every 10°C increase in ambient temperature, the cement hydration rate increases by 2-3 times, and the initial setting time can be shortened by 30%-50%.
• When the temperature is lower than 5°C, winter construction plans need to be initiated, and steam curing or electric heating measures should be adopted to keep the internal temperature of the concrete above 10°C.
• During high-temperature construction in summer, crushed stone aggregates need to be pre-cooled in the mixing water to control the concrete mold temperature not to exceed 30°C.

Adaptation of admixture functions

• Retarders (such as lignosulfonate) can extend the final setting time to more than 20 hours, which is suitable for layered pouring of mass concrete.
• Early strength agents (such as triethanolamine composite systems) can increase the strength by 40%-60% in 3 days, and are often used in emergency repair projects or prestressing.
• Attention should be paid to the compatibility test of admixtures and cement to avoid abnormal phenomena such as rapid setting or excessive retarding.