Excess water is the enemy of high performance concrete and the concrete strength is weaker. Performance chemicals or admixtures play a key role in both concrete strength AND color. Excess water is the enemy of pigment and colored concrete.
Making sure that all the water added can completely react with cement means darker colors and stronger concrete.
Water is required to chemically convert cement powder into a complex crystal lattice multi silicate structure. BUT only enough water should be added to accomplish this chemical reaction. Water is H20 and both H and O are required to chemically convert cement into the silicate structure. Adding more water to create flow or to improve compaction is very common, however it is the absolute worst thing to do from a chemical point of view.
Admixtures are added for a variety of reasons. From the lower price per gallon flavor of the day to super low dosage rates. From a color and pigment perspective, rarely are admixtures used as a chemical to help the chemical bond of the pigment particle within the ITZ zone. While low and very low admixture dosage rates will help control efflorescence and absorption rates, our objective is more focused at the S/A & ITZ zone interface and the attachment and bond of the pigment particles to the silicate structure. When excess water is present, the % of excess water does not get converted in the main chemical reactions taking place. Efflorescence, haze, washed out colors, shrinkage and cracking are all evidence of excess water. Furthermore, the concrete surface is the first to dewater from evaporation so the required water is no longer available to chemically react to the denser silicate phases. This results in a higher calcium hydroxide % which is weaker than the other denser phase silicates.
An admixture designed for colored concrete should accomplish two goals. The first is to reduce the excess water required for flow and to fill molds. The second is to KEEP the water that has been added inside the body of the concrete to allow it to completely react and convert to the multi silicate structures.
This green paver was produced in 1998 using Part B MicroGreen pigments and a performance admixture condition. During manufacturing on the wet side, water could be beaded on the paver surface for several minutes. One half has been weathered for 17 years, the other half is the reference unweathered half in 2015. While some color loss has taken place, it is still green and well within acceptable tolerances and demonstrates how concrete color longevity can be achieved when pigments are used properly.
It's important to understand that Part B pigments cannot be used when excess water is present. The surface tension of excess water combined with the higher surface area of finer Part B pigments requires the use of a high performance condition. This generally means a water/cement (W/C) ratio of less than 0.33.
A high performance admixture condition should be used to help the performance of all these pigments. Many of our customers see the results with stronger concrete, darker colors and the ability to reduce the amount of pigment to achieve a target color. Lower Portland cement consumption and lower batch water consumption will also be important benefits. Clarke MegaMAx TZ and several other specific admixture brands can accomplish these goals. Use less water to make better colored concrete and cement products.