Concrete has a problem with its reputation. Most people imagine it as cold, grey and heat hungry, which makes buildings an oven in summer and an ice box in winter. Precast concrete thermal blocks are made to correct just this cliché. They have the strength of concrete and the insulation of a core and walls no longer act like a highway for heat, they begin to function like a wall. Ever wonder how a solid concrete block can be turned into a component of a building that is energy-saving? Let’s take a look at the entire manufacturing process, step by step.
Thermal Blocks are Different from Normal Concrete Blocks
A typical concrete block is a single solid material from edge to edge. It is strong but has a high thermal conductivity, which means that heat can be transferred through it much more rapidly than through most insulation products.
A precasted thermal block, however, makes that equation change. It is created in layers: normally two layers of concrete known as wythes with a layer of insulation often formed from expanded polystyrene (EPS), extruded polystyrene (XPS) or polyurethane foam in between. This multi-layered design turns out to be the “gold standard” for insulated precast systems, which is why it is being used more and more in research and development.
It creates heat exchange between inside and out less, and gives the building structural muscle. If it’s a concrete block, then imagine the concrete block learned how to wear a jacket!
The Design of the Steps:The Steps Design Thermal Blocks are Different from the Normal Concrete Block
It all begins with the mix. Precast plants aren’t simply picking up any bags of cement and hoping for the best. Based on published research on precast insulated panels, engineers calculate an exact ratio of cement, aggregates, water and admixtures to achieve a desired compressive strength, which in the case of thermal panels is typically more than 15 MPa.
The insulation core material is also determined at this time. EPS and XPS are the most popular options due to their good thermal properties and affordable price; polyurethane foam is used where a thin feel with high thermal resistance is required. There are some high-tech systems that even use vacuum insulation panels that can be ten times as energy-efficient as old-fashioned foam insulation. However, the materials are much more expensive.
The choice has more significance than one might think. If the mix is not correct, or the insulation is wrong, the block will crack under load, or it will be non-insulating. It’s no guesswork that will be going on here, it’s chemistry and engineering shaking hands.
Step 2: Mould Preparation
The mould comes next and this is the easy one. The mould platform is cleaned and all scraps are removed before the release agent is added, to ensure that the block does not struggle to come out of the mould.
Unclean mould = Unclean block. The presence of air bubbles, surface pits and dimensional faults is invariably caused by a poorly prepared mould. This step is taken seriously, just like the chef would do when seasoning a pan before he puts his food on it. Ignore it, and all of the downstream suffers.
Step 3: Reinforcement Placement
Workers place steel reinforcement, typically a welded mesh or rebar cage, within the mould prior to any concrete being poured. This reinforcement is used to provide the block with tensile strength because concrete is strong in compression but weak in bending and pulling.
It also secures and stabilizes any lifting point that will be used later on to assist crews in moving and installation of the block without harming it. The correct placement is important as reinforcement that is too close to the surface may corrode over time and if the reinforcement is placed too deep it will not serve its purpose.
Step 4: Pouring and Vibrating Structural Layer
Now the actual concrete is poured in. The moulds are filled with the outer or inner concrete layer (structural wythe) around the reinforcement cage and the layer is poured first. The concrete is immediately after pouring vibrated by mechanical vibrators.
Vibrating isn’t a procedure for the sake of procedure. It rejects the air from the mix, making the concrete to settle completely around the reinforcement and in all corners of the mould. Otherwise you’ll end up with these poor holes in the block filled with air, known as honeycombing, which weaken the block and provide a convenient path for water entry later.
The Final Step in Installation Is to Place the Insulation Core
After the first layer has been poured and has set, the insulation board or layer of foam is placed on top. This can be achieved by placing rigid EPS or XPS boards directly on the partially-settled concrete or by using a foam or perlite mortar insulation which chemically adheres to the underlying concrete structure.
At this stage, shear connectors, which are small rods or plates of steel, fibreglass or composite are usually inserted through the insulation. These connectors attach the two concrete surfaces together mechanically, rather than gluing 2 concrete slabs together with foam in between.
This layer is responsible for the actual thermal work. This is the one person on the entire block who does all the work of insulating and the concrete takes all the credit for keeping the building standing.
In Step 6, the Second Concrete Layer Was Poured
The second layer of concrete is installed on top of the insulation and connectors, with another vibration to expel air and guarantee compaction. Now the block is virtually complete – concrete, insulation, concrete – with the shear connectors in the middle.
Some manufacturing processes pour this layer after the first layer has already partially cured so that the insulation is not floating in the wet concrete, but instead has a solid base to sit on. Regardless of method, it is the same objective of timely application for the plant’s specific system—strengthening the bond among all three layers.
Step 7: Curing
The only place where patience becomes a part of the product is in curing. Fresh concrete requires time and controlled moisture to reach full strength, and one of the most common reasons for concrete blocks to fail in the long run is to rush this phase.
Usually blocks are cured in a precast plant under controlled temperature and humidity and occasionally with steam curing without compromising strength. Plants typically wait until the block has achieved sufficient early strength to tolerate demoulding and handling – usually within 24 to 72 hours depending upon the mix design and curing technique employed.
Demoulding and Quality Inspection: Step 8
Once the block has cured sufficiently, it comes out of the mould. Time is now. The quality inspectors inspect the surface defects, dimensions and bonding between the concrete layers and the concrete core.
Defective blocks, even if they pass the compressive strength test, are rejected before they leave the plant. This stage of the inspection aims to safeguard the reputation of the manufacturer as well as the future building on which these blocks will form the structure and energy efficiency.
The 9th Step Is Storage and Dispatch.The 9th Step Is Storage and Dispatch
Approved blocks are stored in a natural curing yard until they are ready for transport. The blocks are kept safe in storage areas until leaving for construction sites where the anchor points used during Step 3 are embedded in the blocks to lift them into place.
The thermal block comes to the job site ready to go—mixed, reinforced, poured, insulated, cured and inspected before a single crane picks it up and places it.
This Manufacturing Process Is So Relevant to Us That It Matters
These steps are not taken simply for the sake of ceremonies. Each stage has a direct impact on the performance of the final block in a building. Energy consumption benefits that are significant for insulated precast walls compared with conventional concrete walls have been demonstrated in various studies, some of which have shown a reduction in energy use of nearly half that of the concrete walls, depending on the climate and the thickness of the insulation.
The genuine benefits of precast thermal block production. It’s not about making a block appear finished, but ensuring buildings remain comfortable whilst consuming minimum energy to heat and cool them. Concrete finally has the opportunity to be strong, and smart – and after all, that just about took forever.
