Improve Concrete Strength and Adhesion with a Vibrating Concrete Poker
When a concrete mix is poured into a mould or form, it contains air bubble that can account for up to 20% of its total volume. These bubbles reduce the strength of the concrete, and prevent it from achieving proper adhesion to steel reinforcement rods or mesh. Concrete pokers remove the bubbles, improving strength and adhesion. You can find a wide range of concrete pokers on eBay at low-cost prices.
Why do bubbles reduce the strength and adhesion of concrete?Every bubble in a concrete mix represents a void, and the more voids your concrete has, the less dense and more porous the mix will be. Not only do voids increase water ingress that can cause extensive freeze-thaw damage, they also reduce compressive strength and prevent the concrete from contacting and adhering to reinforcing structures.
How do concrete pokers work?Concrete pokers can measure up to around 2 feet in length and inside the casing is a rotating rod. Eccentrically mounted weights are fitted along the length of the rod and cause the poker to vibrate as the rod spins. The poker is submerged into the freshly poured concrete mix, and the vibrations agitate semi-viscous mass in a small radius around the poker. This allows the air bubbles to rise and the concrete to compact. It also forces any excess water present in the mix to rise to the surface. The poker is slowly extracted as soon as air bubbles stop appearing on the surface of the mix, it is then re-submerged at a distance of around four times the poker's diameter from its last location. This process is repeated until the entire mix has been compacted. It is very important to leave the poker submerged for the correct duration. If the poker is removed too soon, air bubbles will still be present in the mix. If the poker is left submerged for too long this can cause the cement to separate. Pokers function to:
- Remove air bubbles.
- Improve adhesion.
- Improve compressive strength.
How much concrete a poker can compact per hour is determined by two factors: the vibration speed of the poker (VPM), and the outer diameter of the poker. Therefore, this figure varies by model. Higher density mixes also take longer to compact as they are less viscous. Higher vibrations speed pokers are desirable when working with high-density concrete to improve agitation.
