SU697929A1 - Method of determining effective radius of air bubbles in concrete mix - Google Patents

Description

I

The invention relates to the determination of the effective radius of air bubbles in a concrete mix, the size of which affects the frost resistance of concrete.

Under the effective radius understand the average radius corresponding to the average pressure in the bubbles caused by surface forces.

A known method for determining the effective radius of the bubbles, in which the hermetically closed container is filled with water to the upper level of the water tube and through it, compressed air is fed from above. Under pressure, air bubbles in the mixture are reduced. From the magnitude of the compression of the bubbles and the applied pressure, we first calculate the initial pressure in the air bubbles and then their effective radius 1.

The closest in technical essence and the achieved result is a method for determining the effective radius of air bubbles in a concrete mix, including placing the compacted concrete mix in an airtight vessel, filling it with water, measuring

pressure in the vessel and the calculation of the effective radius 2.

The known methods are trumped-off methods, require special adaptations and are also not sufficiently accurate.

The purpose of the invention is to improve the accuracy and simplification of the device, as well as reducing the BpcMeiffl definition by speeding up the air release process.

Claims (2)

The goal is achieved by the method of determining the effective radius of air bubbles in a concrete mix, including placing the compacted concrete mix in a sealed vessel, filling it with water, measuring the pressure in the vessel and calculating the radius eKTHBHoro, placed in a sealed vessel, dilute the concrete mixture and maintain until air is released from it; Additives - cement hydration retardants - are introduced into the water used for liquefaction, and to reduce the time of determination, additives that reduce the viscosity of water are added to the concrete mix which are subjected to vibration. The essence of the method is illustrated in the drawing, which shows a diagram of an instrument for determining the effective radius of the bubbles. Concrete mix 2 is placed in the vessel in the form of a pre-compacted sample or compacted in the same vessel. The vessel is closed with a lid 3 and through openings 4 and 5 when the pressure gauge 6 is closed, the vessel is filled up to the top with water, after which holes 4 and 5 are closed. Then, using agitator 7 or another way, dilute the concrete mix until the bubbles completely break and release. air accumulating in the upper part of the vessel. Using a pressure gauge 6, for example, water pressure, measure the pressure of the sootspout in the vessel, open holes 4 and 5, close the valve of the pressure gauge bis using a burette, supplement the vessel to the top with water, determine the air volume in the concrete mix. Since the air volume before and after dilution of the concrete mix does not change, its average pressure in the bubbles is equal to the pressure in the vessel. The pressure arising from the determination of the effective radius of the bubbles is usually 5-50 HS / cm. Therefore, this method does not require a thick-walled vessel, which simplifies its design. To speed up the process of air release and to reduce the time needed to determine the effective radius of the bubbles, less viscous liquid, such as benzene, is added to the water in which the mixture is diluted. In order to accelerate the release of air in the process of diluting the mixture, it can also be subjected to vibration. In the concrete mixture, during its preparation or in the process of liquefaction, additives that slow down the hydration of cement, such as sugar, are introduced, which reduces or eliminates the effect of cement hydration AND contraction on the volume changes of the liquefied concrete mixture and improves the accuracy of determining the effective radius of the bubbles. Example. Determine the effective radius of the gouzier of a concrete mixture of 1: 1.5:: 2.5 (cement: sand: crushed stone), the compacted volume weight of which is 2300 kg / m. The surface tension of water is 73 gf / cm. A sample of compacted concrete mix weighing 2.3 kg is placed in the device. The vessel through holes 4 and 5 is filled to the top with water. With the tap of the manometer closed, a layer of water is 15 cm. The concrete mixture is diluted with the aid of a stirrer 7, after which the tap of the manometer is opened and the mixture is kept stirring until the level of the liquid in the manometer stops (point b). The pressure in the manometer with the composition of the PM 10 g / cm. and the volume of air in the inlet tube and in the manometer itself, taking into account the decrease in the water level in it from point a to point b, was VT 3 cm. Then, the volume of air in the concrete mixture is determined as B b, for which, with the manometer valve open, holes 4 are poured into the vessel from the burette through the openings 4 and 5 until it is completely filled. The volume of the filled water is V 60 cm. The air pressure in the PC vessel, taking into account the losses in the supply tube and in the manometer (V.,.) And at atmospheric pressure Pd 1033 gf / cm is ... PNvtyVT tV -P V p.. IOj: 60t3l -tl03JJ - L5l6 0 47 HS / cm. 60 The effective radius of the bubbles in the concrete mix is 26-2.7310 3.1-10 cm., Which is close to the results usually obtained by direct determination under a microscope in hardened concrete. Thus, this method in comparison with the known method improves the accuracy of determining the effective radius of air bubbles in the concrete mix and simplifies this process. Claim 1. A method for determining the effective radius of air bubbles in a concrete mix, including placing a compacted concrete mix in an airtight vessel, filling it with water, measuring pressure in the vessel and calculating the effective radius, characterized in that, in order to improve accuracy and simplify the definition, in a hermetic vessel, the concrete mixture is diluted and held until air is released from it. 2. The method according to claim b, which, in order to increase the degree of accuracy of the determination, is added to the water used for liquefaction, additives-retarders of cement hydration. 3. The method according to W1.1 and 2.0 tons of this and that in order to reduce the determination time due to the acceleration of air release, additives are introduced into the water used to liquefy the concrete mix. || Viscous water viscosity or concrete mix is subject to vibration. Sources of information taken into account in the examination 1. Lazarev, AD, et al. A method for determining the content of air pores of different radii in a freshly compacted concrete mix. Proceedings of NIIZHB, vol. 29, 1977. 2. Handbook of road construction materials. Edited by Gorelysheva N.V.W., Transport, 1972, p. 244-245. 2/1 but H 6 t t