Soluble Silica Source for Low-Temperature AAC Curing
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Solution Overview
Problem
The production of autoclaved aerated concrete (AAC) is hindered by high energy consumption and carbon dioxide emissions due to the steam curing process, which requires elevated temperatures and pressures, limiting the use of alternative silica sources with higher solubility that could reduce energy usage and binder content.
Innovation Solution
Using a silica source comprising at least 50 wt% soluble silica species, such as amorphous silica or water glass, and reducing the steam curing temperature to 100-170°C, while adjusting the calcium/silicon molar ratio to low values, to produce AAC with high compressive strength and reduced energy consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If quartz is used as silica source, then high solubility is achieved, but high steam curing temperature (>180°C) is required
Solution Approach 1:
The patent changes the chemical composition parameter of the silica source from quartz (low solubility) to soluble silica species (high solubility, ≥50 wt%). This parameter change enables the steam curing temperature to be reduced from >180°C to 100-170°C, directly resolving the contradiction between achieving high dissolution and reducing energy consumption.
2Loss of time
If quartz is used as silica source, then high steam curing temperature is required, but shorter curing times and lower binder content cannot be achieved
Solution Approach 1:
By changing the silica source parameter from quartz to soluble silica species, the patent enables shorter curing times at lower temperatures. The high solubility of soluble silica species accelerates the dissolution rate, allowing the steam curing process to be completed faster and at lower temperatures, thus resolving the contradiction between curing time and temperature.
3Strength
If soluble silica materials are used, then shorter curing times are expected, but sufficient strength values and lower binder content could not be achieved until today
Solution Approach 1:
The patent optimizes the calcium/silicon molar ratio parameter to low values (0.4-0.7) when using soluble silica species. This parameter optimization, combined with the high solubility of the silica source, enables sufficient tobermorite formation and CSH phase development, achieving high compressive strength (≥1.5 MPa) with reduced binder content, thus resolving the contradiction between strength and binder content.
4Strength
If high steam curing temperature is used, then high compressive strength is achieved, but high energy consumption and CO2 emissions result
Solution Approach 1:
The patent changes the silica source parameter to soluble silica species with ≥50 wt% soluble silica content, which enables the steam curing temperature to be reduced to 100-170°C. This parameter change maintains high compressive strength (≥1.5 MPa) while significantly reducing energy consumption and associated CO2 emissions, thus resolving the contradiction between strength and energy consumption.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach results in AAC with exceptionally high compressive strength, lower binder content, and reduced energy consumption, enabling the use of a broader range of silica materials and potentially replacing quartz, thus saving resources and reducing CO2 emissions.
Implementation Method 1
The dissolution behavior of different silica raw materials can be very different. Quartz has a relatively low solubility in water and the rate of dissolution is also relatively slow. Therefore, in the case of using quartz as a silica source in AAC, steam curing with a quite high temperature i.e. more than T>180° C. is required. However, with silica sources which have a higher solubility in water compared to quartz, there is a possibility to achieve lower steam curing temperatures.
Implementation Method 2
The autoclaving process includes hydrothermal treatment of a mixture at elevated temperature, typically around 180-200° C. and pressure of 12-13 bar, under saturated steam condition.
Implementation Method 3
The main components to produce AAC are silica sand as SiO2 source, lime, and cement as a CaO source. The steam curing process is necessary first to dissolve the silica raw material and second to establish the conditions for CSH formation.
Data Source
AI summary
The present invention relates to an autoclaved aerated concrete having a content of tobermorite of at least 12.5 wt % and a content of amorphous CSH phases of at least 30 wt %, based on the total weight amount of autoclaved aerated concrete, the process for producing said autoclaved aerated concrete using a silica source, which comprises a soluble silica species and a low curing temperature and the use of a silica source, which comprises a soluble silica species for the production of an autoclaved aerated concrete.