Will the Owner Get the Floor He Expected__tcm45-348560

8/22/2019 Will the Owner Get the Floor He Expected__tcm45-348560

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W hat aspects of a floor can theowner reasonably expect to

be guaranteed and what aspects isit safe for the contractor to guara n-tee? Predictability of operations andc o n t ractor competen ce are at theheart of these questions. At the pre-sent the best prediction of the per-f o rmance of a floor is based on ane valuation ahead of time of thequality of the materi a l s, the con-c rete mix pro p o rt i o n s, the job spec-ifications and the reputation of the

floor constructor.Sh o rtly after its construction and

early use, some of the chara c t e ri s-tics of a floor will become appare n t .It will be known whether the floor isf ree of dusting, whether there hasbeen any plastic shrinkage cra c k i n g , whether the floor is plane and whether it has proper slope ford rainage if such a slop was speci-fied. Any discoloration pro b l e m s will also appear early.

Most cracks first appear as finehairlines after one to seven days butsome cracks might not develop fora year or more. Cracking andspalling at joints from the action of wheeled vehicles or failure of thes u b g rade may begin at almost any age depending on the quality of thefloor or subgrade and the seve rity of the tra f f i c.

Wear resist ance

It takes a long time to evaluate the

wear resistance of a floor. Un f o rt u-n a t e l y, the contractor may not befully informed about the ultimateuses and abuses of the floor until af-ter it has failed. A number of testsm e a s u re the wear resistance of con-c rete floors. Most of these invo l vethe application of loaded, mov i n g steel wheels, ball bearings or abra-s i ve discs. Each produces its part i c-

ular type of wear although nonequite conforms to the wear of con-c rete floors in serv i c e. Some of thesemachines can be taken to the joband used to test a floor in place; oth-ers are applicable only to test speci-m e n s.

Troubleshooting

Changes in materi a l s, pro c e d u re sand workmanship may be neces-s a ry to remedy problems in floorc o n s t ruction. Common tro u b l e s

and possible causes are listed below.

Rapid wear:

• mix of too low strength for tra f f i ca n t i c i p a t e d

• mix too we t

• adding water to the surface whenf i n i s h i n g

• pre m a t u re floating and trowe l i n g

• improper curi n g

• floor not designed for service ex-

p o s u re

• floor opened to traffic too soon

• surface frozen at early age

Cracking:

• low strength mix

• mix too we t


• improper placement of re i n f o rc e-m e n t

• poor subgrade pre p a ra t i o n• too great a distance between con-

t rol joints

• inadequate curi n g

• insufficient depth of contro l j o i n t s

• fre eze-thaw action causing scal-i n g

• chemically initiated expansion

• expansion of re i n f o rcement ru s t-ed because of inadequate con-c rete cove r

Curling:

• slab too thin

• joints too far apart


Plastic shrinkage cracking:

• dry subgra d e

• use of unsaturated absorptive ag-g regates in mix

• high winds

• high air and concrete tempera-t u re s

• low re l a t i ve humidity

• too rapid eva p o ration before set-t i n g

Poor quality: when it will appear, how to remedy it, what to learn from it.

Will the owner get the floor he expects?

This floor was built wit h no joints andno provision for curing. The firstcracks appeared within a week.



Dusting:

• too much clay in the aggre g a t e s

• troweling dry cement into surf a c eto dry it


• In vented heaters

• finishing while bleed water is onsu rf a c e

• construction debris ground intosu rf a c e

Light or dark spots:

• va riations in water-cement ra t i o

• contamination in the mix

• presence of cement balls fro mpoor mixing

• troweling dry cement into sur-face to dry it

• surface set over re t a rded con-c re t e


• use of calcium chlori d e

• polyethylene curi n g S c a l i n g :

• troweling dry cement into sur-face to dry it

• surface set over re t a rded con-c re t e


• improper bonding in two-coursef Bo o r s

• fre ezing and thawing of concre t e with inadequate or no air con-t e n t

• fre ezing at early age

Crazing:

• too much clay in the aggre g a t e s

• too rapid vibra t i o n

• ove ruse of jitterbugs, vibra t i n g

s c re e d s, darbies or bull floats• pre m a t u re floating and trowe l i n g

• troweling dry cement into surf a c eto dry it

• improper curing (use of curi n g water that is much colder thanthe concrete slab)

• intermittent wet curing and dry-i n g

Blisters (some combination ofthe following factors):

• subgrade cooler than the con-c re t e

• air content too high

• cement content too high• too much sand fines in air- e n-

t rained mix

• mix so lean that it must be work e de xc e s s i ve l y

• too early setting of plastic con-c re t e

• winds blowing over fresh concre t esu rf a c e

• rapid eva p o ration of water fro mc o n c rete with low bleeding ra t e

• sealing the surface while the un-derlying concrete is still plastic

Repairing crack s

Eve ry economical crack re p a i rmethod leaves some evidence of thec rack. One method of repair is tosaw out a section of concrete oneach side of the crack, clean thee d g e s, brush a neat cement gro u tinto the sawed surfaces and re c o n-c rete the intervening area. Ep ox y c o n c rete also can be used. If the

patch borders or straddles a joint afull-depth joint should be built intothe new concrete to allow for in-evitable future move m e n t .

Another method entails widening the joint with a power router to pro-duce a wedge-shaped opening about an inch wide, which is thenfilled with a joint sealant. Wheret raffic is heavy, the sealant must bereplaced peri o d i c a l l y. Ap p e a rance isra rely satisfactory.

Na r row nonworking cracks may be re p a i red by injecting them withan epoxy grout. This method is de-s c ribed in Co n c rete Co n s t ru c t i o n ,May 1972, page 221.

Repairing plastic shrinkagecracking

Once plastic shrinkage cra c k s

h a ve hardened in the surface littlecan be done to eliminate them. Fo r-tunately this cracking seldom de-c reases the strength of the floor al-though it is unattra c t i ve and dirtcatching. Plastic shrinkage cra c k sm a y, howe ve r, eventually becomed rying shrinkage cracks in floorsfour inches thick or less. In these

c a s e s, after shrinkage is completeand the cracks are at their widestopening the surface can be ro u g h-ened and a thin-bonded concre t etopping applied. Small cracks canbe filled with a va rnish or epoxy of the proper viscosity squeeged in.

Correct ing dusting floors

Chemical or l iquid floor hard e n-ers frequently are used to corre c tdusting floors. Details are given inthe ACI 302 St a n d a rd. These hard-

eners are likely to reduce but noteliminate the production of dust.Floor hardeners will not make agood floor out of a bad one but they may prolong the floor’s life and util-i t y. Dusting floors also may be im-p roved by grinding down to exposea harder laye r.

Sometimes the trouble ascri b e dto dusting of the concrete is actual-ly the working free of mud, mort a r,l i m e, gypsum, paint or other debri sthat has been ground into the sur-

face during construction. If deter-gents and power scrubbers fail tos o l ve the problem it may be neces-s a ry to apply a we a r- resistant coat-i n g .

Correct ing improper slope

Un d e s i red slope in a stru c t u ra lslab or insufficient or inaccura t eslope in a stru c t u ral floor withd rains may be caused by careless ori n a c c u rate setting of screeds orf o rm s.

If the elevation perm i t s, suchslopes can be corrected by toppings.Thinner toppings re q u i re so thin asection or featheredging at the low-er end of the slope that a perm a n e n tbond is difficult although possible with an epoxy topping.

If settlement of the subgra d e



causes improper slopes it is neces-s a ry to provide uniform support be-f o re correcting with a topping.

Removing discoloration

Di s c o l o ration may result fro mt rowel burn s, admixt ure s, stainsf rom organic materi a l s, lime con-c e n t rations built up from the gre e n-

house effect of curing membra n e sor the va riety of debris that may bec a relessly dropped on the floor dur-ing construction. Calcium chlori d emay accentuate trowel burn s, whichsometimes can be re m oved by ap-plication of sodium hyd rox i d e. Limec o n c e n t rations may wash away with water if treated ve ry promptly buto t h e rwise re q u i re solutions of amild acid or light sanding. Eve n t u a l-l y, some lime spots will wear away.Re m oval of t hese kinds of discol-

o ration is described in CO N C R E T ECO N S T RU C T I O N , November 1967,page 417.

O rganic stains may succumb toapplications of poultice materi a l ssuch as clay, fly ash, or diatoma-ceous earth together with solve n t sa p p ro p riately selected for this pur-p o s e. (For more details on stain re-m oval see Co n c rete Co n s t ru c t i o n ,May 1961, page 132.) Light ru b b i n g with a silicon carbide stone may succeed with shallow stains.

PUBLICATION #C730540Co py right © 1973, The Ab e rdeen Gro u p All rights re s e rve d

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Will the Owner Get the Floor He Expected__tcm45-348560