Accelerating of setting and hardening

High-Energy mixed (HEM) and hand mixed mixtures were tested with an effort to find out

Penetration resistance of two mortars with and without Fly Ash admixture.

Materials and proportions

White Portland cement Type 1 “Lehigh Co”, and Sand for All Purpose

“Quikrete Co” as well as Fly Ash of Cayuga AES was used for two mixes.

The equal workability of mortars has been achieved with HRWR admixture “Sika Viscocrete 3010”.

The proportions of ingredients by weight:

Cement / Sand / Water / HRWR = 1 / 2 / 0.343(for hand mixing) / 0.0076. In case of High-Energy mixing, the quantity of water has been increased 12% to avoid the rapid setting of mixture during process of mixing.

With Fly Ash as supplemental cementitious material, the proportions were as follows:

Cement / Fly Ash / Sand / Water / HRWR Admixture = 1.0 / 1.0 / 2.0 / 0.75 / 0.017-0.023. In this particular case High-Energy mixing required an increased quantity of admixture.

Energy consumption

HEM mortar with Fly Ash – 9.5 W-h / kg of mixture (6 min)

HEM mortar without Fly Ash – 6.5 W-h / kg of mixture (3.5 min)

Temperature

The ambient temperature 24-26^oC (76^o-78^oF)

The temperature of hand mixed mixture 21-23^oC (70^oF)

The initial temperature of HEM mixtures 35-40^oC (94-104^oF).

The hydration of Portland cement with HEM is more intense than in the case of hand mixed mortar.

High-Energy mixing actively accelerates setting and hardening of the mortars. Time of initial setting of the mortar without Fly Ash is around 2 hours (500 psi of penetration resistance). Adding Fly Ash to substitute half of Portland cement may successfully increase it. The time of initial setting increases to 12-14 hours.

Therefore High-Energy mixing with the inclusion of Fly Ash creates a possibility to reduce cement consumption and successfully manage the setting and hardening of concrete that is important in hot weather conditions. It is possible with HEM to overcome the dehydration process mechanically accelerating cement hydration to achieve the effect of bonding water molecules in place of evaporation.

The strength development of HEM mortars and concretes.

E-mail: vfrid38@comcast.net