HaConcrete is everywhere: buildings, roads, sidewalks, bridges and the foundations of almost any structure imaginable. We produce more concrete than any other material on the planet, and the amount is increasing, especially with global developments in China and India. Cement is the powdered binder that binds sand and crushed stone into concrete, making it one of the most energy-intensive products on the planet. The limestone used is fired at temperatures up to 1,450 degrees Celsius (2,640 degrees Fahrenheit) in huge kilns that use only fossil fuels. The chemical reactions involved produce even more carbon dioxide as a by-product. 1kg of cement produces 1kg of CO2 into the atmosphere. Every year around the world, the production of cement and concrete generates as much as 9% of her CO2 of all humans.2 emissions.
Society has manufactured cement and concrete in much the same way for a century. Tests have shown that a portion of the cement in the mix can be replaced with calcined (calcined) clay or components made from waste such as fly ash or slag, resulting in lower emissions without loss of strength. increase.Not enough supply to meet demand, but such alternatives can reduce CO2 To some extent.
Other alternative materials and processes can significantly reduce emissions. Some are already spreading. Others are experimental. Since most cements and concretes are made locally or regionally near their place of use, the availability of alternative materials, revised building codes to permit their use, capital costs for retrofits, and the market The acceptance of all is a practical task.
better cement production
Cement production consumes large amounts of energy, much of it from fossil fuels that emit CO.2Some steps also emit CO2 directly, in particular, the creation of limes (step 3) hardener clinker (step 4). Replacing fossil fuels with renewable energy sources and increasing the efficiency of your overall production can reduce your carbon footprint by up to 40%. By using different raw materials for clinker, the remaining 60% of carbon emissions can be significantly reduced. (The process shown is for so-called dry kilns, which have widely replaced wet kilns, which use more energy.)
1. Limestone mining and crushing
Usage: Calcium carbonate-bearing deposits such as limestone and chalk are mined from quarries and may contain small amounts of clay containing silicon, aluminum, or iron. The ingredients are crushed into pieces of 10 cm or less, and then further crushed into powder and called raw meal.
Room for improvement: Start with basalt instead of limestone, or use “carbon-negative limestone” produced with waste CO2 (step 2), reducing emissions by up to 60-70%.
2. Preheat the raw food…
Usage: The raw meal in the upper chamber of the kiln is heated to 700 degrees Celsius by the kiln’s hot, swirling exhaust gases, driving off moisture.
Room for improvement: Burn oxygen-rich air to reduce CO2 emissions. Add equipment to capture CO2This can reduce emissions by up to 60%.Use of waste CO2 Making carbon negative limestone (step 1). Burn biomass or waste to heat the kiln instead of fossil fuels.
3. …and turn your diet into a lime
Usage: The preheated meal is fired at 750-900°C in the upper and inner combustion chambers of the kiln, converting calcium carbonate to calcium oxide (quicklime) and CO.2This step accounts for 60-70% of the CO.2 It consumes approximately 65% of all fuels emitted from raw materials and used throughout the cement manufacturing process.
Room for improvement: Burn oxygen-rich air to reduce CO2 emissions. Add equipment to capture CO2Reduce emissions in steps 2, 3 and 4 by 30-40% by using electric kilns that run on renewable energy.
4. Turn lime into clinker
Usage: Lime is burned at temperatures up to 1,450°C in kilns rotating 3-5 times per minute. This process dissolves lime and sinters (fuses) it into Portland cement clinker (dark gray nodules 3-25 mm in diameter) that emits more CO.2Clinker is a binder that reacts with water to harden cement.
Room for improvement: Mineralizers such as calcium fluoride and calcium sulfate are added to lower the lime melting temperature and save energy.
5. Cool and store the clinker
Usage: The hot clinker is grated, where it is cooled to around 100°C by a fan. When it cools, it is stored in silos and can be used for a long time without deterioration, so it may be sold as a unique commodity.
Room for improvement: Electrify the process or pipes with the waste heat from step 3 for initial cooling.
6. Blend the clinker and plaster
Usage: Clinker is mixed with gypsum in a 20 or 25 to 1 ratio.
Room for improvement: Electrify the process.
7. Grind the blend into Portland cement
Usage: A roller mill or ball mill grinds clinker and gypsum into a fine gray powder known as Portland cement.
Room for improvement: Add finely ground limestone to replace up to 35% of the cement and reduce emissions generated during the early manufacturing stages. This mixture is known as Portland limestone cement. By adding fly ash (20-40 percent), slag (30-60 percent), or calcined clay (20-30 percent) to reduce the clinker-to-cement ratio, reducing emissions by a similar percentage: Create a “mixed cement”.
8. House cement in silo
Usage: The powder is mixed well and stored in silos. Pack in retail bags or load onto trucks bound for a concrete mixing facility.
Room for improvement: Consider low-carbon alternatives to Portland cement for specific applications. These alternatives include alkali-activated cements and biocements produced by algae or microorganisms, and cements made from magnesium phosphate, calcium aluminate, or calcium sulfoaluminate. Such options can reduce overall process emissions by 40% or more.
better concrete production
Concrete is usually made at or near the construction site. Optimizing the structural design can reduce the amount of concrete needed (step 3). Reuse and processing of concrete after demolition (step 4) can absorb CO2 It offsets some of the emissions from the original cement production.
1. Mix cement, water and aggregate
Usage: Cement is made by mixing a certain amount of water with an aggregate such as sand, gravel or crushed stone at ambient temperature to reach the desired fluid consistency. About 80% of the mix is aggregate.
Room for improvement: Convert conveyors and mixers to run on renewable electricity, significantly reducing emissions. Additives such as biochar and algae are added to increase concrete strength, adjust workability and curing time, and reduce emissions by 1-5% or more.
2. Transport to site
Usage: Concrete is mixed in a drum mixer truck and transported to the construction site.
Room for improvement: Switch to electric trucks. Minimize, collect and upcycle waste concrete into other precast materials such as highway barriers.
3. Build the structure
Usage: The building design determines the required shape, volume and strength of the concrete elements.
Room for improvement: Optimize structural design to avoid wasting concrete. Switch from specifications that require a minimal amount of cement in concrete to specifications that require a specific compressive strength that can reduce the required cement content. Change building codes to allow new alternative cements and blended cements. It relies on concrete’s ability to gain strength over time by specifying compressive strength in two or three months rather than the more common one month which can reduce the amount of material required.
4. Disposal plan
Usage: Demolished concrete is often dumped in landfills or crushed and used as a substrate for roads and highways.
Room for improvement: Design for disassembly so that all or part of the concrete elements can be reused.If the concrete has been demolished, the concrete should be crushed and spread thin to maximize surface area and exposed to air for as long as possible to absorb CO.2Over years of exposure, concrete can probably absorb as much as 17% CO.2 It is discharged when manufacturing cement for the concrete.
