Thirsty concrete, also known as permeable or pervious concrete, is a porous paving material designed to let water pass through it directly into the ground, preventing puddles and urban flooding by reducing surface runoff. It achieves this by eliminating fine sand from the mix, creating interconnected voids (like tiny tunnels) that allow rainwater to drain rapidly into a gravel base, recharging groundwater and filtering pollutants.
It's very labour intensive on-site work – and it can take a long time. You also have to wait for the concrete to cure before you can can load it. This method can easily be out of tolerance (at around +-20mm) In order for your team to work safely, you'll need a large excavation site.
This material is typically produced at a utility sluice pond site by dumping raw ash into the pond and allowing it to hydrate and harden into a working platform. Additional raw ash is placed on top of the platform in thin lifts, watered, compacted, and allowed to hydrate and harden.
As a result, pervious, thirsty, or porous concrete was developed for long-term roadway construction, consisting of cement, coarse aggregate (9.5mm to 12.5mm), and water with little or no fine aggregate. Key Words: Groundwater infiltration, Pervious concrete, Stormwater, coarse aggregate and fine aggregate.
The 20/30/40 rule in concrete is a simple guideline for mix proportions, suggesting roughly 20% cementitious materials, 30% water + admixtures (for workability), and 40% aggregates (sand and gravel), providing a good balance for quality and economy. While often linked to a broader 10-20-30-40 rule (10% cement, 20% water/air, 30% sand, 40% gravel by volume), the 20/30/40 emphasizes the key component percentages for a practical mix, especially for achieving good strength and pumpability.
Fast-setting concrete is ideal for setting posts because there's no mixing—you simply pour the dry concrete from the bag right into the hole, then add water.
The "90-minute concrete rule" was a standard guideline (ASTM C94) requiring ready-mix concrete to be discharged from the truck within 90 minutes (1.5 hours) of mixing to ensure workability and quality, but this rule has been updated, allowing for custom time limits to be set by the purchaser and producer, acknowledging modern admixtures that extend working time, though the original principle of limiting time to maintain quality remains crucial.
Gravel is one of the most affordable alternatives to concrete driveways. It is also easier to install and maintain, but may require that more gravel is added and smoothed over time.
Types of Concrete
Here's a quick guide: Opt for precast when your project requires consistent quality, quick installation, or involves large-scale, repetitive elements. Choose in-situ if your project demands bespoke designs, seamless structures, or has budget constraints that prioritise lower upfront costs.
Proper precast concrete manufacturing can reduce these risks, and installation can help as well. But cracking is a natural risk for precast concrete, and one of its difficulties as a material.
Precast concrete methods favour the reuse of formwork, and off-site manufacturing allows most manufacturing waste to be recycled. Precise quantification and dimensioning further reduces waste.
Spray: To maintain the proper moisture levels, concrete should be sprayed with water frequently. This is known as moist-curing. Most specialists recommend watering the slab 5 to 10 times per day for the first seven days. Moist-cured concrete can be up to 50% stronger than dry-cured concrete.
Though concrete is strong, it is porous. So when salt enters the concrete, it can cause damage. The reason behind this is that salt lowers the freezing point of water, leading to a repeated freeze-thaw cycle. This cycle can significantly weaken the surface of the concrete.
A 20x20 foot concrete slab generally costs between $1,600 and $4,800 installed, averaging around $2,400-$3,200, depending heavily on thickness (4" vs. 6"), site prep, rebar, and labor rates, with 4-inch slabs on the lower end and 6-inch reinforced slabs higher; expect about $4 to $8 per square foot for basic material and installation, but costs rise with complexity.
AshCrete. Fly Ash is a byproduct of combustion of coal which was previously discarded in the landfill, but is now used for manufacturing green concrete. AshCrete is a substitute for traditional concrete that heavily utilizes recycled fly ash.
Decomposed granite is a type of gravel made from 100% pulverized granite. This type of gravel is ground into fine particles and will pack together to form a gravel that hardens like concrete when compacted.
The 10-20-30-40 rule for concrete is a simple guideline for mix proportions by volume: approximately 10% cement, 20% water and trapped air, 30% sand, and 40% gravel (coarse aggregate), serving as a basic rule of thumb for typical concrete. The goal is to use as much inexpensive, strong aggregate as possible, with just enough cement paste to bind it, using smaller particles to fill voids for a dense, efficient mix.
It takes about 24 to 48 hours for the concrete to set, but after 4 to 8 hours, it begins to harden. After about 6 hours, the potential damage from rainwater will not be as significant as the concrete begins to dry. However, it will still be best to take precautions to prevent getting damaged concrete.
Concrete should be placed into its final position as soon as practicable. Extended delays in placing can lead to a significant loss of consistence with time making it impossible to place with satisfactory compaction.
Remember that you don't need a plug to screw into, you can screw directly into the concrete. It is also important to note that you can remove a concrete screw. Many people make the mistake of assuming that because a concrete screw is for heavy duty applications, it is a permanent fixing.
Cement mixed with water can handle minor repairs, but only becomes strong, versatile concrete when combined with aggregates.
Can my neighbour attach things to my fence? The simple answer to this one is no. If you're the fence owner, your neighbour cannot attach anything to the fence without permission. They shouldn't be nailing, drilling, screwing or sticking anything to the structure without asking you first.