In t e g rally colored concre t e ?D o n’t expect a burst of enthusi-asm when you ask your re a d y

mixed concrete producer to supplyit. His phone will probably ring firstif the results are n’t as expected. Bu tsteps can be taken by the contra c-t o r, concrete pro d u c e r, and colorsupplier to help ensure that attra c-t i ve and uniform results are ob-tained with integral color.

Co n c rete that’s colored all the wayt h rough can be used in walls as we l las flatwork. The color can’t wear off.And exposed aggregate or deep-b roomed finishes are possible be-cause the concrete is colore dt h ro u g h o u t .

Either raw pigments or pigmentscombined with other admixture scan be used to give integral color.The coloring materials can be pur-chased in bulk quantities (50-poundbags are commonly used) or in pre-m e a s u red sizes to make batchinge a s i e r. For instance, a 9-poundpackage of pigment might be addedfor each bag of cement used in abatch. If a less intense color we red e s i red, a smaller sized packagecould be used.

Liquid color systems have alsobeen developed. Pigments are sup-plied in a liquid suspension whichmakes batching easier, especially onwindy days.

To get good results with integra l l yc o l o red concre t e, pay particular at-tention to the following details.

Mix design

• Use a minimum cement contentof 470 pounds per cubic yard (a 5-bag mix).

• Aim for the lowest slump that canstill be placed and finished re a d i-ly and don’t exceed a 5-inchs l u m p. Adding extra water to in-c rease slump may cause exc e s s i vebleeding and nonuniformity inc o l o r.

• Avoid using any admixtures thatcontain calcium chlori d e. Ca l c i-um chloride may cause salt de-posits to form on the concre t es u rface and discolor it.

• For air- e n t rained concrete sub-jected to fre ezing and thawing, bea w a re that some coloring agentssuch as carbon black will re d u c eair content. The amount of air-e n t raining admixture may have tobe increased to keep the air con-tent at desired leve l s.

• For large pro j e c t s, make a mock-up wall panel or slab that re q u i re sat least 3 cubic yards of concre t e.Use the same cement brand, ag-g regate type, and constru c t i o nmethods that will be used on thej o b. If necessary, make adjust-

ments in the amount of coloradded before the project gets un-der way. Special color blends tomatch existing stru c t u res or spe-cific color needs are available inb a t c h - s i ze packages.

Batching and mixing

• D o n’t add the color pigment first.It may stick to the mixer bafflesand not get uniformly distri b u t e d .The best sequence is to first batchsome of the aggre g a t e, bothcoarse and fine, and water. Wi t hthe mixer running, add the colorand mix for at least a minute be-f o re adding the balance of materi-a l s. Tu rn the drum at mixingspeed for an additional 3 to 5minutes before the truck leave sthe yard .

• If pigment is batched from larg eb a g s, always use a whole numberof bags per truck. Don’t try tobatch partial bags.

• On jobs re q u i ring more than onet ruckload of concre t e, use thesame size truck for each load.This is especially important if col-or is batched from large bags. Ifyo u’re using three 50-pound bagsfor a 10-yard load, switching to an8 - y a rd truck will re q u i re using ap a rtial bag of color pigment. Im-p recise batching of color pig-ments almost always causes va ri-

Tips on integrally colored concreteBY RICHARD BUEHRER

GROUP DIRECTOR OF PIGMENT COLORS

TAMMS INDUSTRIES

ITASCA, ILLINOIS

ations in color.

• D o n’t change cement brands inthe middle of a job. Cements fro md i f f e rent sources are differe n tshades of gra y. Changes in ce-ment color cause changes in thec o n c rete color.

• Watch slump particularly closelyd u ring batching. Slump va ri a-tions often indicate that watercontent has changed, perhaps be-cause of cleanout water left in thet ruck or changes in the aggre g a t es u rface moisture content.Changes in water content alsocause color va ri a t i o n s.

• Consider the possibility of usingliquid color systems. Liquid col-ors are easier and faster to batchand provide easier storage andhandling. They also disperset h roughout the concrete faster.

Forming and placing concretefor vertical surfaces

• Seal joints in forms for ve rt i c a ls u rf a c e s. Water leakage at jointscauses changes in water- c e m e n tratio and discoloration near thel e a k .

• Use a nonstaining form re l e a s eagent and thoroughly clean form sb e f o re reusing them. Re m n a n tcement from dirty forms can stainc o l o red surf a c e s.

• D o n’t allow heads of internal vi-b rators to touch the form s. Thiscauses dark spots called vibra t o rb u rn s.

• It may be necessary to pre c o n d i-

tion new natural grain woodf o rms before they’re used on aj o b. This can be done by coatingthem with a cement slurry that al-so contains the pigment to beused, then re m oving the coating.

• Make sure that any steel, whetherrebar or snap ties, has at least 11⁄2inches of concrete cover to pre-vent stains caused by corro s i o n .

Finishing and curing flatwork

• D o n’t start finishing colored con-c rete until the bleed water hase va p o rated. Finishing too earlycauses discoloration and a we a k ,n o n d u rable surf a c e.

• Use mechanical floats or trowe l sif possible. The one-way motionof the blades creates a more uni-f o rm colored surface than theb a c k - a n d - f o rth motion used inhand finishing. Move edgers inone direction only to produce am o re uniform color.

• Co n c rete in the sun sets at a dif-f e rent rate than concrete in thes h a d e. This may cause differe n c e sin color. If possible, time the pourto avoid having sunlit and shad-ed are a s.

• D o n’t add water to the surf a c ed u ring finishing opera t i o n s.Added water may create a blotchys u rf a c e.

• Use a liquid membrane curi n gcompound. Cu ring with water,wet burlap, plastic sheets, or wa-t e r p roof paper can cause color tobe nonuniform.

PUBLICATION #C870445Co py right © 1987, The Ab e rdeen Gro u p

All rights re s e rve d