introduce
Introducing many uniformly distributed microwave bubbles into cement slurry can improve the durability of concrete subjected to freeze-thaw cycles. When frozen, as long as the size and spacing of the pores are within a certain range, the ice formed in the capillary pores will expand into adjacent pores without causing cracking. The size of the pores is represented by the specific surface area, which refers to the ratio of the surface area to the volume of the pores. The ratio of surface area to volume of pores. The spacing between pores is called the dispersion coefficient, which is related to the maximum distance between any point in the cement slurry and the free surface (around the pores).
Ordinary concrete needs to form freeze-thaw cycle resistant concrete with a maximum dispersion coefficient of 0.20mm. Practice has proven that the use of air entraining agents, excessive vibration, chemical additives, or high water pressure can easily alter the pore structure. The characteristics of pores are determined based on the microscopic determination of the porosity coefficient of ASTM C457 hardened concrete. This analysis requires taking a hardened concrete sample, which undergoes coring, sawing, polishing, infiltration, preparation, and observation under a microscope in the laboratory.
The following image is a polished sample prepared for ASTM C457 analysis.

The AVA pore analyzer can detect the pore structure in mixed concrete in just 15 minutes. It can be tested during the trial production, transportation to the site, or immediately after pouring. Therefore, the characteristics of pores can be quickly controlled to ensure the quality of concrete. Once the specific surface area or dispersion coefficient does not meet the requirements, remedial measures can be taken immediately.
The AVA porosity analyzer and many ASTM C457 analyses are related as follows:
BriteEuram Project No: BE-3376-89, Task 2 "Evaluation of Pore Quantity and Quality in Freshly Mixed Concrete", Federal District Office, Hua, USA
Shengdun's usual conclusion is that, in terms of specific surface area and dispersion coefficient, the results obtained by AVA technology are completely consistent with those obtained by ASTM C457 method.
AVA testing principle
Releasing bubbles from cement slurry into the liquid, as long as the liquid has a certain viscosity and hydrophilicity, the number and size of bubbles can be preserved.
After being released from the cement slurry, bubbles rise to the surface, and according to Stroke's law, large bubbles rise faster than small bubbles.
The bubbles reaching the surface are recorded and their weight is measured. Based on the weight, the distribution of pores and specific surface area can be calculated. Moreover, for a given amount of water
Mud and concrete can determine the dispersion coefficient of air content and pores.
AVA testing steps
1. Connect the drill to the vibrator, and the vibrator will vibrate the sampler into the concrete to obtain a 20cm cement slurry sample. Aggregates larger than 6mm will be removed
Fall off.
2. Collect the sample into a syringe and inject it into AVA liquid.
3. AVA liquid automatically stirs for 30 seconds, releasing gas and reaching the underwater vessel connected to the recording balancer through the container.
4. After 25 minutes of analysis, the test is over, and then the data is calculated and the results are printed as follows:

AVA-3000 configuration
Computer, testing software, cement slurry sampler (3 pieces), driller, testing fluid, power supply, testing base, columnar riser, windshield, ordinary mixture mixing needle, hard mixture mixing needle, piston, buoyancy disk, electric drill, funnel, sample plate, USB connection cable, power cord, rubber suction ball, bottled silicone oil, pipe mounted silicone grease, operation manual, water tank with temperature regulator and mixer, upper cover (2 pieces), 2L container (2 pieces), aluminum carrying case (2 pieces)