Dew-Point Thermometer for Cement Self-Desiccation Testing
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Solution Overview
Problem
Conventional methods for testing the self-desiccation effect in cement-based materials are limited by the precision and reliability of hygrometers, which struggle to measure relative humidity accurately above 99% and require long equilibration times, making it difficult to assess autogenous shrinkage and potential cracking in early stages of cement-based material setting.
Innovation Solution
A testing method using a dew-point thermometer and capillary negative pressure tester to measure the internal relative humidity and negative pressure changes in cement-based materials from final set to water addition, leveraging thermodynamic equations to calculate relative humidity changes, allowing for continuous monitoring of self-desiccation effects during hydration and chemical shrinkage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a conventional hygrometer is used to test internal relative humidity, then measurement precision is improved, but the equilibration time becomes too long and cannot measure early stage humidity above 99%
Solution Approach 1:
The patent replaces the conventional hygrometer (which uses mechanical/electrical sensing elements requiring long equilibration) with a dew-point thermometer that measures temperature based on dew-point formation. This substitution enables rapid measurement of relative humidity above 99% without long equilibration times, as the dew-point method directly detects the temperature at which condensation begins, providing immediate readings even in early cement stages.
Solution Approach 2:
The patent changes the measurement parameter from direct humidity sensing (which saturates above 99% RH) to temperature measurement of the dew-point. By measuring the temperature difference between the dew-point sensor and ambient temperature, the system calculates relative humidity using thermodynamic relationships, enabling accurate measurement in the 99.98%-99.5% RH range where conventional hygrometers fail.
2Adaptability or versatility
If a tensiometer principle is used to test pore negative pressure, then measurement capability is extended, but it cannot measure the self-desiccation process from final set to water addition
Solution Approach 1:
The patent embeds the dew-point thermometer probe into the cement-based material during mixing or placement, before the material sets. This preliminary action ensures the sensor is positioned within the material's pore structure from the beginning, allowing continuous measurement of the dew-point temperature and calculation of relative humidity from the moment of water addition through final set and beyond, capturing the complete self-desiccation process that tensiometers miss.
Solution Approach 2:
The patent substitutes the tensiometer principle (which measures negative pressure mechanically) with a thermodynamic approach using dew-point temperature measurement. This substitution enables measurement of relative humidity changes corresponding to negative pressure changes from 0 to 80 kPa and beyond, covering the entire period from water addition through final set, whereas tensiometers only capture conditions after final set when negative pressure reaches 80 kPa.
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
Enables accurate and continuous measurement of relative humidity changes between 99.98% and 99.5% within the first day after water addition, providing a comprehensive understanding of water consumption and self-desiccation processes, thereby addressing the limitations of conventional testing methods and offering a quantitative basis for self-desiccation analysis.
Implementation Method 1
uses the dew-point thermometer to test the internal dew-point temperature of the cement-based material from final set to being shaped after addition of water for 1d and afterwards the relative humidity is calculated according to the equation (3)
Implementation Method 2
a negative pressure tester for capillary using the tensiometer principle is used to test the negative pressure of the capillary
Implementation Method 3
Laplace's equation: γ refers to the gas-liquid interfacial tension, θ refers to the contact angle, r refers to the critical pore radius, ΔP refers to the negative pressure of capillary
Implementation Method 4
Kelvin's theorem: pg refers to the saturated vapor pressure of the curved surface water inside pore, p sat refers to the saturated vapor pressure of the plane water
Data Source
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AI summary
The present invention discloses a testing method for self-desiccation effect on cement-based material. This method is able to test the humidity change of the cement-based material from final set to water being added for 1d so as to show the water consumption and self-desiccation process inside the cement-based material. The testing method for self-desiccation effect on cement-based material is to test the internal dew-point temperature of the cement-based material from final set to water being added for 1d, and afterwards to calculate the internal relative humidity of the cement-based material according to the equation (3). The testing method provided by the invention can test the humidity change of the cement-based material from final set to water being added for 1d so as to represent the water consumption and self-desiccation process inside the cement-based material. In addition, a testing method with different stages and covering the whole process is further provided to test the whole process of the relative humidity gradually falling from 100% when the cement-based material is shaped after addition of water under an enclosed condition. Consequently, it provides a theoretical basis for quantitative calculation of self-desiccation of the cement-based material.