DD216540A1 - METHOD FOR DETERMINING THE STRENGTH DEVELOPMENT OF CERTAIN CEMENT EXPOSURE SYSTEMS - Google Patents

Abstract

The invention relates to a method z. Analysis of the state change of upgrading cement aggregate systems caused by procedural and structural effects by means of ultrasound. Ultrasound signals are continuously transmitted through a moertel mixture or concrete mix, their transit time is measured and the ultrasonic velocity-time characteristic is developed. The inflection point of the time curve serves as a guideline for the prognosis of the expected compressive strength curve. The process is non-destructive, whereby fluctuations in the composition of the cement aggregate systems and the hardening conditions can be registered and the resulting changed strength profile can be recorded. The method can be used for optimum control of concrete hardening.

Description

Title of the invention

Method for determining the pestness development of hardening cement aggregate systems

Field of application of the invention

The invention relates to a method for predicting the course of the pestness development of structural cementing, hardening cement aggregate systems.

Characteristic of the known technical solutions

The solidification of plastic concrete mixtures is subject to certain laws and regulations that are only to a limited extent qualitatively and quantitatively foreseeable. Traditional test methods of fresh and pest concrete properties are still important, but only inadequately highlight the kinetic aspect of structure formation. Thus, the manufacturer lacks real information about the pattern formation processes and thus about the course of pest development. An effective design of the concrete hardening is therefore impossible. So far, the strength Ent-, winding concrete mixes, which is a function of the time, temperature and material composition, generally previously determined on test specimens.

«Η π r η jfi O 1. * -4 Λ Π ß * Ä (I

It is assumed that the same concrete strength is achieved when the product of hardening temperature and hardening time assumes the same values. The required standard values (number of hours) are determined on test specimens and transferred to the production of concrete products of most different component dimensions. The same methodology is used for the Controlling the strength development of concrete by means of ultrasound · 40 50 test specimens of corresponding material composition are produced, sonicated under the respective temperature conditions and subjected to the mechanical pressure strength test »From the values obtained a calibration curve is created (sound velocity value is assigned to the respective compressive strength), which is used as the basis is used for testing the strength development on the component

However, the values determined by these methods for the control and optimization process on the component to be manufactured are often falsified, since the determination of the compressive strength of the component concrete at any time on the basis of comparison measurements on specimens is at least associated with an error of +15 % . The physico-mechanical properties of the concrete in the finished part deviate considerably from those in the test specimen, since differences already occur during introduction and compression. In addition, the curing conditions prevailing in practice (temperature, air humidity and the like) can not be simulated in the laboratory unpredictable. In addition, the material composition of a concrete mixture can not always be kept constant, especially with larger components. Measurements of the electrical resistance on hardening concretes have not proven to be advantageous since extreme values can be measured, but these can not be clearly assigned to characteristic phases of the hardening process are. In addition, the electrical conductivity is influenced by a variety of factors in an uncontrollable manner.

Capacitance measurements on hardening silicate building material screens have a very narrow scope of application due to the energy losses occurring.

Object of the invention

The object of the invention is to predetermine the course of strength development of cement aggregate systems directly on the consolidating component, thereby enabling monitoring and optimal control of the hardening process. /

Explanation of the essence of the invention

The invention has for its object to develop a method to determine the expected course of compressive strength in the early stages of concrete hardening. According to the development of strength of hardening cement aggregate systems is predicted by ultrasound pulses are sent through building structures, components or samples at certain intervals whose duration is measured and from the ultrasonic velocity-time dependence is determined from the change, in particular the maximum change, the compressive strength of the hardening system is predetermined.

The velocity of an ultrasonic pulse through a hardening cement stone, mortar or concrete mixture initially remains almost constant (curve I in Pig. 1.0 ^ Lt ^ t-), increases during the structure strengthening phase in proportion to the hardening time (± 2 = S t stJ and After reaching the state where the deformation resistance of the substance begins to increase more slowly than the compressive strength, it again strives for a constant value (t> * t ^).

It has surprisingly been found that there is a close relationship between the ultrasonic velocity-time dependence (curve I in Pig. 1) and the pestness development (curve II). The criterion is the inflection point P ^, i. the point of maximum increase in ultrasound speed

The development of the speed of sound and the compressive strength as a function of the hardening time are governed by the uniform process curve in Pig.

O, 32tr

The rise and thus the course of v (t) and R (t) in the concrete Pail depends on the relative time V. PUr the compressive strength is:

^ Compressive strength = (5,43 -JL) ¹ » ⁰¹ . (2)

Because the maximum increase in ultrasonic speed and compressive strength at the same time

V ^{tf (3)}

the course of the individual hardening phases and the development of compressive strength can already be predicted in the early stage of concrete hardening · Changes in the material composition of the concrete mixes and changed hardening conditions are registered and the corresponding change in the pest history is recorded. · Pur transient hardening conditions (with constantly changing temperature) , the expected strength development can be predicted using a differential equation defined by the process variables ά, _ and t, "on

W W

Turning point is determined · (Pig · 3) ·

The following applies:

CXw ultrasound =% 22 ⁽⁴⁾

'. _# . , w.

OCw compressive strength = ^ ² ^ (5)

For the determination and evaluation of the ultrasound velocity, a device is suitable, which includes in its complex a microcomputer with screen unit, an ultrasound device and corresponding test heads.

embodiment

The invention will be explained below on an exemplary embodiment:

It is predicted the strength development of a hardening gravel concrete. The binder used is PZ 1/40. The cement quantity is 331 kg / m, the water cement value = - = 0.5. Shortly after dressing, compacting and insertion

Z of the mixture, the ultrasonic vibrators are coupled to the concrete. Thereafter, the continuous transit time measurement of Ultraschallimpulae, which go through the concrete. The speed of sound changes depending on the hardening time (Pig. 4). The inflection point of the ultrasonic speed-time graph is registered after 14 hours. According to relations (1), (2) and (3):

= 14 hours,

5,523,

.1329

The hardening time of 28 days then becomes 0.9505. Thus, after 14 hours, a strength development of 13.9%, based on the 28-day value is achieved. The strength development after 1,3,7 and 14 days is shown in Table 1.

Table 1

Hardening time (d)

27.8

3 62.9

7 81.6

14 90.3

Claims (1)

Claim of invention, A method for determining the strength development of hardening cement aggregate systems by means of ultrasound, characterized in that ultrasound pulses are sent at certain time intervals, the transit time is measured by building structures, components or samples, and from the change, in particular the maximum change in the ultrasonic velocity in dependence Time the compressive strength development of the hardening system is predetermined * For this 3 sheets of drawings λ λ η α Ο Cl