Key Considerations for Designing Effective Construction Joints in Concrete Floors

Con­struc­tion joints play a crit­i­cal role in ensur­ing the sta­bil­i­ty and integri­ty of con­crete floors and oth­er struc­tures. They must be designed prop­er­ly, tak­ing sev­er­al fac­tors into consideration.

Design­ing Effec­tive Con­struc­tion Joints in Con­crete Floors

Impor­tance of Con­struc­tion Joints in Con­crete Floors

When installing con­crete floors, your con­struc­tion team will first cre­ate joints unless the con­crete slab is small. When the pave­ment area is wide and large, pour­ing the slab at once is impos­si­ble. Hence, con­struc­tion teams cre­ate con­struc­tion joints to divide the area.

A con­struc­tion joint can be formed using a bulk­head made of pre­cast con­crete, wood, met­al, or oth­er mate­ri­als. These joints deter­mine where to start and stop pour­ing and cur­ing con­crete; they are also called planned con­struc­tion joints. Con­trac­tors have already con­sid­ered and pre­pared the loca­tions and details of planned con­struc­tion joints.

The pur­pose of con­struc­tion joints is to facil­i­tate con­struc­tion. How­ev­er, this joint can also serve as a con­trac­tion joint. Con­struc­tion joints are formed before pour­ing con­crete. Mean­while, con­trac­tion joints are placed in the fresh con­crete. The pur­pose of the con­trac­tion joint is to con­trol crack­ing, which is a com­mon issue with con­crete floors. This issue com­pro­mis­es the structure’s integri­ty and appear­ance. But it’s impor­tant to remem­ber that a con­trac­tion joint can­not be a con­struc­tion joint.

Prop­er­ly designed con­struc­tion joints in con­crete will help reduce the num­ber of ran­dom cracks in the con­crete floor, mak­ing floor main­te­nance eas­i­er and less cost­ly. They will also strength­en the floor and make it look more appealing.

More on Con­struc­tion Joints

When it comes to con­struc­tion joints, you must under­stand butt-type, key­way, and dow­el bars.

A butt-type con­struc­tion joint is typ­i­cal­ly applied when the heav­i­est loads on the slab are light vehi­cles and foot traf­fic. It’s sim­ple: one con­crete slab is poured direct­ly up to anoth­er slab. The con­nec­tion at the top of the two con­crete slabs is edged main­ly for aesthetics.

On the con­trary, a key­way con­struc­tion joint is the most com­plex type. This joint type serves as the slab edge for the pour and holds the two slabs togeth­er when a force push­es one of the slabs ver­ti­cal­ly. It typ­i­cal­ly takes time to build and install a wood­en, metal­lic, or plas­tic key­way into the form­work. It’s usu­al­ly applied in com­mer­cial set­tings but is not rec­om­mend­ed for load transfer.

Oth­er con­struc­tion joints come with dow­el bars. Dow­el bars are short steel bars that mechan­i­cal­ly con­nect slabs while still allow­ing hor­i­zon­tal move­ment. They allow the slab to assume some of the weight before the load goes on it, increas­ing the load trans­fer efficiency.

Fac­tors to Con­sid­er When Design­ing Construction/​Contraction Joints

Gen­er­al­ly, the design of construction/​contraction joints will depend upon the struc­ture type, con­struc­tion method, and join­ing mate­ri­als available.

Envi­ron­men­tal Factors

Con­crete moves when tem­per­a­ture changes. It con­tracts when the tem­per­a­ture drops and expands when the tem­per­a­ture ris­es. These tem­per­a­ture vari­a­tions will deter­mine the spac­ing of joints. If you pour con­crete in the sum­mer, the joint may be fur­ther placed apart to accom­mo­date the expan­sion. If con­struc­tion takes place in win­ter, the joints may be clos­er to avoid exces­sive compression.

Anoth­er con­sid­er­a­tion in spac­ing is mois­ture con­tent vari­a­tion. The dimen­sion of con­crete changes when it gives up or absorbs mois­ture. Mois­ture affects the con­crete when it’s dry­ing out and after it has already hardened.

Joint­ing Material

Joint­ing mate­r­i­al is anoth­er crit­i­cal con­sid­er­a­tion when design­ing construction/​contraction joints in con­crete floors. In addi­tion to the mate­r­i­al used to make the joint, there’s also the joint filler, seal­ing com­pound, and water bar.

Joint Filler

As the name sug­gests, joint filler is for fill­ing joints in struc­tures. How­ev­er, this strip of com­press­ible mate­r­i­al doesn’t just fill the gap; it also allows the joint com­po­nent to move freely with­out devel­op­ing com­pres­sive stress due to ther­mal and oth­er changes. It also sup­ports the joint sealant.

Joint fillers come in many types, and the best choice will depend on the struc­ture. For garage and fac­to­ry floors, joint fillers must pre­vent the ingress of for­eign mat­ter. If the con­crete floor will be exposed to out­door ele­ments, the filler should have excel­lent resis­tance to weathering.

Joint Sealants

On the oth­er hand, joint sealants pre­vent water, air, and oth­er envi­ron­men­tal ele­ments from enter­ing or exit­ing the struc­ture. Many joint sealants are avail­able on the mar­ket; it is impor­tant to use one specif­i­cal­ly for­mu­lat­ed for con­crete floor­ing. Oth­er con­sid­er­a­tions when select­ing a sealant include the joint design, adhe­sion, and phys­i­cal and chem­i­cal properties.

Oth­er impor­tant con­sid­er­a­tions are appli­ca­tion and instal­la­tion. It’s cru­cial to deter­mine the sealant’s con­sis­ten­cy, appli­ca­tion tem­per­a­ture range, and com­pat­i­bil­i­ty with oth­er materials.

Water Bar

Water is an ene­my of con­crete. Mois­ture can pen­e­trate the con­crete floor through mul­ti­ple sources, such as ground mois­ture or water, rain­fall, and cap­il­lary action. Water ingress can lead to var­i­ous issues, such as crack­ing, reduced con­crete strength, and cor­ro­sion of steel rein­force­ments. That’s why installing a water bar is cru­cial if the con­crete joint is sub­ject to ground­wa­ter pressure.

What Hap­pens When Con­struc­tion Joints Are Poor­ly Designed?

A poor­ly designed con­struc­tion joint on con­crete floors will most like­ly result in pre­ma­ture crack­ing. This hap­pens because the con­trac­tors either used the wrong mate­r­i­al or placed the joints incor­rect­ly. Cracks in con­crete floors can weak­en the struc­ture and cause addi­tion­al damage.

Cracks can reduce the con­crete floor’s load-bear­ing capac­i­ty, weak­en its ten­sile strength, and com­pro­mise sta­bil­i­ty. Addi­tion­al­ly, cracks can make the floor less appeal­ing. While cracks can be fixed, the process costs mon­ey and time. It’s gen­er­al­ly more cost-effec­tive to design and install con­crete joints prop­er­ly than to deal with pre­ma­ture cracks and asso­ci­at­ed expenses.

Sur­face Prepa­ra­tion of Con­struc­tion Joints

Prop­er sur­face prepa­ra­tion of a con­crete con­struc­tion joint is cru­cial before pour­ing new con­crete. It just involves clean­ing. Dirt, fine par­ti­cles, and loose aggre­gate accu­mu­late on the sur­face, and they can pre­vent the con­crete from bond­ing, so they must be removed. Depend­ing on what’s on the sur­face, the fol­low­ing clean­ing meth­ods can be used:

• Chem­i­cal clean­ing, which involves the use of deter­gents and oth­er chemicals.

• Mechan­i­cal clean­ing, which uses rotary and impact devices.

• Blast clean­ing, which includes sand­blast­ing, shot blast­ing, and water blast­ing. The lat­ter uses a high-pres­sure water jet to clean the con­crete surface. 

• Wire brush­ing and wash­ing, which are also com­mon meth­ods that can clear surfaces.

In addi­tion to clean­ing, the sur­face should be rough­ened to ensure that the joints will bond well. It also needs to be wet with clean, potable water before plac­ing new concrete.

Choose Kaloutas for Qual­i­ty Con­crete Floor Installation

Joints must be designed and installed prop­er­ly. Gen­er­al­ly, engi­neers review the prepa­ra­tion of con­struc­tion joints before pour­ing the con­crete and are present when the joints are placed. The con­trac­tor needs only to fol­low direc­tions and noti­fy the engi­neer of activ­i­ties con­cern­ing the joint.

Nev­er­the­less, con­trac­tors must still be knowl­edge­able about con­crete joints to ensure the integri­ty and sta­bil­i­ty of floors. At Kaloutas, all con­crete floor­ing installers are cer­ti­fied in all phas­es of con­crete prepa­ra­tion. They under­go in-house train­ing to ensure they are equipped with the tools and knowl­edge nec­es­sary to com­plete a job prop­er­ly the first time. Every­one is ded­i­cat­ed to ensur­ing top-qual­i­ty work with­out caus­ing too much trouble.

If you need more tips for design­ing con­struc­tion joints in con­crete floors or want to know what the require­ments for con­crete joints are, don’t hes­i­tate to con­tact the Kaloutas team today.