Wha are Concrete Popouts?| What Causes Concrete Popouts | How To Repair Popouts in Concrete?
What are Concrete Popouts?| What Causes Concrete Popouts | How to Prevent/Avoid Concrete Pop outs
Wha are Concrete Popouts?
A “popout” is a tiny, often cone-shaped depression in a horizontal concrete surface caused by the expansion and fracture of a near-surface aggregate particle.
Generally, a portion of the shattered aggregate particle will be discovered in the bottom of the cavity, while the remainder will remain adhered to the pop out cone’s point. The cavity’s diameter might range from 14 inch (6 mm) to a few inches.
The majority of popouts appear within the first year of installation. Popouts induced by alkali-silica reactivity (ASR) can occur from a few hours to several weeks, or even a year, of the concrete being put.
Popouts caused by moisture-induced swelling may develop immediately after placement as a result of the plastic concrete’s absorption of water, or they may not show until after a season or year of high humidity or rainfall, or after the concrete has been subjected to freezing temperatures.
What Causes Concrete Popouts?
Generally, popouts are caused by a porous aggregate with a high absorption capacity but a low specific gravity. Moisture is absorbed by the vulnerable aggregate
In the winter, the moisture freezes, expands, and exerts internal pressure on the aggregate, causing it to break.
When the offending aggregate collects moisture or freezes in damp conditions, it expands, generating internal pressures sufficient to breach the concrete surface.
Popouts are frequently caused by pyrite, hard-burned dolomite, coal, shale, soft fine-grained limestone, or chert.
Popouts may also occur to alleviate pressure caused by the uptake of water by the expanding gel formed by the chemical reaction between the alkali hydroxides in the concrete and the reactive siliceous aggregates.
How to Prevent/Avoid Concrete Pop outs
To limit or eliminate concrete pop outs, the following procedures can be taken:
- Whenever possible, use concrete with the lowest possible water content and slump for the application.
- Use a concrete made of crushed stone or aggregate material.
- Cover the surface with plastic sheets after screeding and bullfloating to prevent evaporation prior to final finishing in hot, dry, and windy conditions. This lowers alkali migration to the surface as a result of drying, hence reducing popouts induced by alkali-silica reactivity (ASR).
- Do not finish concrete that still have surface bleed water.
- Avoid using a hard-steel trowel where it is not necessary, like as on the majority of outside slabs.
- Avoid the usage of vapor barriers. To reduce friction between the base material and the slab, cover the vapor barrier with 100 mm (4 in.) of compactible granular fill that has been mildly dampened and choked off with a fine-grade substance. This material should be sufficiently dry to act as a blotter for the concrete that will be poured on top of it.
- Immediately after final finishing, use wet-curing procedures such as continual water sprinkling, fogging, ponding, or covering with wet burlap. Wet-cure for a minimum of seven days, as wet cures can significantly minimize or eliminate ASR popouts. Avoid using plastic film, curing paper, and especially curing compounds, which allow alkalies to accumulate on the surface. Before final drying, flush curing water from the surface. Avoid impervious floor coverings or membranes, as they can exacerbate popout development.
- Where popouts are produced by alkali-silica reactivity, employ a blended cement or a supplemental cementitious material such as fly ash (proved to control ASR). Additionally, using a low-alkali cement is good.
- Construct a two-course structure with clean, sound rock as the topping and the problematic aggregates as the foundation slab, minimizing the vulnerable aggregate’s exposure to excessive moisture.
- Slope the slab surface to provide optimum drainage.
- Use the air-entrained concrete
Is It Possible to Avoid Concrete Pop outs?
The majority of popouts are visual defects that have no bearing on the structural integrity of the structural elements.
However, a high number of popouts allows the entry of water and other toxic chemicals into the concrete, which can eventually result in other types of deterioration, such as corrosion of steel reinforcement.
How To Repair Popouts in Concrete?
Prior to starting a repair work, it is recommended to determine the cause of the popouts by collecting core samples containing one or more typical popouts and submitting them to a certified petrographer for analysis.
Popouts can be fixed by chipping away the residual aggregate particle in the surface cavity, cleaning the resulting void, and then filling it with a proprietary repair material such as a dry pack mortar, epoxy mortar, or other appropriate material according to the manufacturer’s recommendations.
Popout surfaces can be fixed. A minor patch can be created by drilling out the spalled particle and filling the resulting void with dry-pack mortar or another suitable patch material.
If a surface has a large number of popouts that cannot be repaired individually, a thin-bonded concrete overlay may be employed to restore uniform appearance