Sealing expansion joints in concrete floors

Parking garage expansion joint repair

Sealing expansion joints

Sealant for expansion joints

Sealing concrete joints

 

Real Project

Project Data

• Sydney, Australia.

• Multilevel parking.

Our colleagues, the team at Waterstop Solutions NSW in Sydney, have recently completed several expansion joint sealing repairs.

Problems with expansion joints in the parking lot

• One example is the entrance ramp to a multi-level car park where the joint sealant was peeling off the edges of the expansion joint.

• The damaged connection not only affected the aesthetics of the parking lot, but also created a potential hazard for the movement of vehicles and pedestrians.

• Also, a damaged seam allowed water to seep into the parking lot below.

 

Sealant peeling in expansion joint

• Therefore, if this damaged connection between concrete slabs is not sealed, further water damage is likely to hasten the destruction of the rubber bushings in the building joint and in turn damage the concrete structure.

• Another possible consequence is prolonged dripping of soda water.

• This means that tenants may find themselves in a position where they will not be able to use their parking spaces, as they risk damage to the paintwork of cars, stains, damage to other people's property, and these are already financial costs that no one needs.

Causes of joint problems in concrete slabs

Joints between concrete slabs, expansion joints, are subject to many factors that affect their design and service life, throughout the life of the facility.

Under existing conditions, such as at the entrance and exit of a car park, in a commercial or high-rise apartment building, the service life of the joint may not correspond to the declared parameters.

• The general failure of the concrete structure, the formation of cracks, the spalling of concrete and the ingress or infiltration of water, affect the durability of the object.

• Effective placement and sealing of concrete joints are very important design aspects to ensure that concrete slabs remain intact and structurally sound.

The main mistakes in sealing expansion joints with sealant

Insufficient filling depth and incorrect sealant ratio

• The sealant ratio should be 2:1 (width:depth).

• The ratio is a very important aspect, because if you fill the seam to the wrong depth, then the sealant will not be thick enough to stretch and it will crack in the middle.

• And if you fill the seam to a depth greater than necessary, then internal stress is created and the sealant is also torn in the middle.

• When finishing the smoothing of the sealant, it is necessary to create a meniscus shape, in the form of a crescent, for the seam to work properly.

The ability of the internal molecular structure of a material to remain unified during movement is called the cohesive strength of a sealant.

 

Scheme of installation of a seam in industrial floors

Incorrect choice of sealant, regarding its physical and mechanical characteristics or "Not calculated"

Namely: the elasticity of the sealant, the modulus of elasticity of the sealant, Shore hardness and adhesive strength.

Sealant elasticity

• This is the ability of sealants to increase in length and then return to their original size.

• Elasticity is characterized by the relative elongation. 

• Its limits are expressed as a percentage of the nominal size. 

• A sealant with a 200% elongation capability is able to stretch to double its original size without cracking or tearing. 

• Since this measure of destruction is the limit, the sealant is not intended for use up to such an elongation. 

• They are designed to work with only a fraction of this ability, with the added safety factor in mind. 

• Sealant stretched to its limit will not return to its original shape or size. 

• Thus, it will cease to function correctly if it is stretched to its maximum elongation value.

 

Seam work in industrial floors

Modulus of elasticity of the sealant

• This is the ratio of stress to strain. 

• It is measured as ultimate tensile strength, expressed as a given percentage of elongation in kilograms per square centimeter. 

• The modulus of elasticity is directly related to the deformation capacity or elongation.

• Low modulus sealants, having a tensile strength below 4 kg/cm2, have greater elongation than high modulus sealants.

• High tensile strength, gives less deformation ability, in other words, soft sealants, stretch better than hard sealants

• Low modulus, high elongation sealants are required in joints where significant movement occurs.

Shore Hardness

• This is the resistance of a material to penetration from the outside, measured with a calibrated hardness tester.

• This property becomes important when choosing sealants that are subjected to loads as a result of movement, such a situation occurs, for example, in horizontal joints on bridges and our industrial floors. 

• A hardness value of 25 corresponds to soft rubber, and a hardness value of 90 corresponds to a rubber mallet.

The ideal sealant should be stiff enough to withstand traffic, have good abrasion resistance, resilience to absorb shock and maintain joint edges.

Should be soft enough to expand and contract as the joint moves due to shrinkage and/or thermal changes.

Sealant adhesive strength

• This is the ability of a sealant to adhere to a particular substrate, maintaining adhesion during the deformation of the substrate. 

• The adhesive strength of the sealant differs significantly depending on the type of substrate. 

• Therefore, you should contact the manufacturers for samples to test for adhesion to the intended surfaces of application.

• Adhesive failure occurs when the sealant loses its adhesion to the substrate.

• Adhesive failure usually occurs due to an unsuitable primer for the sealant to a particular substrate or due to its absence. 

• In addition, the cause of adhesive destruction is the lack of proper preparation of the seam, the incompatibility of the sealant and the base, and incorrect calculation when designing the seams.

 

Parking garage expansion joint repair

The results of the examination of the condition of the expansion joint in the parking lot

• Judging by the photo, it’s purely my opinion, at the beginning, the sealant began to collapse in the middle of its structure, which indicates an incorrect ratio when filling and sealing the seam.

• It is also possible that it began to break down due to the low-modulus configuration (too soft) and the inability to withstand mechanical stress from car wheels.

• And only then, weak adhesion, the most visible result in the photo is the peeling of the sealant from the edges of the seam. 

• It is likely that the concrete, on both sides of the joint, was not prepared properly (mechanical preparation, cleaning, dedusting), and also the lack of a primer, therefore, the sealant came off.

Solution for the repair and sealing of an expansion joint | Parking garage expansion joint repair

Here's how Waterstop Solutions updated the entry ramp seam design.

We decided to use a polyurethane sealant to seal the expansion joint, observing all the physical and mechanical characteristics of the material, as well as the preparation and application parameters.

Of course, I would consider the option of sealing the seam system using an overlay profile for an expansion joint, since the previous material did not cope, I would give a chance to another solution, but apparently in Australia they also save money and there is a budget. 

Stages of work on sealing the expansion joint

• Removed the existing sealant from the seam, mechanically.

• Prepared the surface by sanding and removing all residues of the old sealant.

• I removed all the dust with an industrial vacuum cleaner.

 

Removing the sealant from the expansion joint

• The polypropylene support rope, closed cell, was set to the correct depth to create the correct 2:1 (depth to width) ratio.

• We glued the seam along its length with masking tape and primed the edges of the seam with a polyurethane primer.

• Filled the joint with a strong, high performance, flexible, UV resistant, non-sagging polyurethane sealant that forms strong adhesion to the concrete substrate and has excellent joint movement characteristics, averaging 25%.

• Removed excess sealant and removed tape.

• Warranty: 12 months.

 

Sealing the expansion joint in the parking lot

It turns out that in Australia, expansion joints are sealed, as in Ukraine.

"Seal the expansion joints in the parking lot effectively"