Low-pH Cement Composition With Early Strength and Better Flow
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Solution Overview
Problem
Existing cementing materials used in high-level radioactive waste disposal repositories, primarily based on common Portland cement, face challenges such as high viscosity, low early strength, high plastic shrinkage cracking risk, and pH values exceeding 11, which are not adequately addressed by adding large amounts of silica fumes, affecting crack plugging and chamber backfilling efficacy.
Innovation Solution
A low-pH value cementing material composed of common Portland cement, silica fumes, a pH value regulator (nano-silicon dioxide, anhydrous powdery calcium chloride, aluminum potassium sulfate dodecahydrate, and calcium stearate), and a water-reducing admixture, with adjusted proportions to achieve a pH of 11 or less within 150 days, improving mechanical properties and fluidity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If large amounts of silica fumes are added to common Portland cement to reduce pH value, then the pH value decreases, but the material exhibits high viscosity, low early strength, and high plastic shrinkage cracking risk
Solution Approach 1:
The patent changes the chemical composition parameters by introducing specific pH value regulators (calcium chloride, aluminum potassium sulfate, calcium stearate) in controlled proportions (0.1-5% each) to reduce pH value without using excessive silica fumes. This parameter adjustment allows achieving pH ≤ 11 while maintaining early strength and fluidity
Solution Approach 2:
The patent creates a composite cementing material system combining common Portland cement with multiple functional additives: silica fumes (5-30%), pH value regulators (calcium chloride, aluminum potassium sulfate, calcium stearate), and water-reducing admixtures. This composite approach balances pH reduction with mechanical property maintenance
2Object-affected harmful factors
If large amounts of silica fumes are added to common Portland cement to reduce pH value, then the pH value decreases, but the material exhibits high viscosity and poor fluidity
Solution Approach 1:
The patent adjusts the water-cement ratio and introduces water-reducing admixtures to optimize fluidity while using controlled amounts of pH value regulators to achieve the desired pH reduction without excessive viscosity increase
Solution Approach 2:
The patent uses water-reducing admixtures as intermediaries to improve fluidity and compensate for the viscosity-increasing effect of silica fumes and pH value regulators, enabling proper material flowability for construction applications
3Strength
If common Portland cement is used as base material, then the material has good mechanical properties, but the pH value remains above 11
Solution Approach 1:
The patent extracts and removes excess calcium hydroxide (the source of high pH) from the cement hydration products by adding pH value regulators that chemically consume Ca(OH)2, thereby reducing pH value while preserving the mechanical strength-providing C-S-H gel structure
Solution Approach 2:
The patent converts the harmful high pH environment into a beneficial low pH environment (≤11) by using pH value regulators to consume excess calcium hydroxide, transforming the alkaline byproduct of cement hydration from a harmful factor into a controlled parameter that meets repository safety requirements
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
The cementing material effectively reduces pH to 11 or less within 150 days, enhances early compressive strength by up to 69.3%, improves fluidity, and maintains or increases compressive strength at 3, 7, and 28 days, meeting the requirements for high-level radioactive waste disposal repositories.
Implementation Method 1
add active materials to consume calcium hydroxide generated during cement hydration
Implementation Method 2
adding large amounts of silica fumes (more than 40% by weight) into common Portland cement can be reduced to less than or equal to 11
Implementation Method 3
a series problems of large viscosity, low early strength, high plastic shrinkage cracking risk
Data Source
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AI summary
The present invention belongs to the technical field of building materials, and discloses a low-pH value cementing material and a preparation method therefor. The method comprises: modifying a common Portland cement clinker by using a pH value regulator, fly ash or ground granulated blast furnace slag, and silica fumes, so that the cementing material simultaneously meets the requirements of pH value less than 11 and mechanical property in the construction of a high-level radioactive waste disposal repository. The material is prepared from the following raw materials in parts by weight: 60-65 parts of the common Portland cement, 0-10 parts of the fly ash or ground granulated blast furnace slag, 25-35 parts of the silica fumes, 3-5 parts of the pH value regulator, and 0.5-1.5 parts of a water-reducing admixture. The cementing material prepared by the present invention has a pH value of 10.50-10.95, a speed of pH value reduction and an age of pH less than 11 can be adjusted by changing an addition amount of the modified material, and the mechanical property of the material is improved. The cementing material disclosed by the present invention can be used to provide support for constructing an internationally advanced high-level radioactive waste disposal repository in China, and has a very high application value.