IE74385B1

IE74385B1 - Lightweight aggregates for reduced-density concretes and method for obtaining them

Info

Publication number: IE74385B1
Application number: IE162691A
Authority: IE
Inventors: Maximilian Wicki
Original assignee: Fibrasa Holding S A
Priority date: 1990-05-18
Filing date: 1991-05-13
Publication date: 1997-07-30
Also published as: GR920300012T1; IE911626A1; ES2028754T3; FR2662155A1; DK0457634T3; FR2662155B1; DE69122426D1; DE69122426T2; GR3022204T3; EP0457634A1; PT97702A; ES2028754T1; PT97702B; EP0457634B1; ATE143655T1

Abstract

The granulate, such as vermiculite, is treated by spraying the surface of the particles with the help of a mixture of three adjuvants, namely a surface-active agent, a setting accelerator and a cement-fluidising agent, as a mixture in water, and the mixer for the preparation of the granulate comprises a rotary central shaft 7 passing through a stationary feed hopper for particles 1, carrying a perforated rotating tray 3 through which passes a liquid feed conduit 6 ending in a spraying nozzle 8. <IMAGE>

Description

LIGHTWEIGHT AGGREGATES FOR REDUCED-DENSITY CONCRETES AND METHOD FOR OBTAINING THEM Description J The present invention relates to lightweight artificial or non-artificial aggregates with increased * density-reduction capabilities for producing non-load bearing, reduced-density concretes. It also relates to a method for preparing coated aggregates.

In the production of reduced-density concrete, the use is known of lightweight aggregates such as expanded schists and clays, pumices, pozzolana, perlites and vermiculites, expended polystyrenes, wood chips and cork.

Such aggregates, which have a density of less than 1, are preferable pre-calibrated by eliminating the fine fraction, for example those particles less than 1.4 mm in diameter, for avoiding a too large amount of additive being absorbed which would be prejudicial to the desired characteristics of the material.

Such aggregates are principally characterized by a high porosity with respect to conventional heavy aggregates. High porosity leads to undesirable properties in the production of a lightweight concrete which is compact and has good mechanical strength. In effect, high porosity provides the lightweight aggregate with a high capacity to absorb water, thus making it necessary to use large amounts of water for correctly hydrating the cement and obtaining concrete that has good workability.

The use of large amounts of make-up water introduces in its turn other disadvantages such as a reduction in mechanical characteristics and an increase in the setting and drying time of the concrete along with poor workability of the concrete and a danger of the cement segregating out.

The present invention enable lightweight aggregates to be obtained which have an improved density-reducing capacity for non-load-bearing concrete, and of which the /HOOD amount used per meter cubed of concrete is reduced, thus enabling the amount of cement used to be increased without leading to a variation in the density of the hardened concrete, along with better workability of the fresh concrete for a reduced make- up water-.cement ratio.

Such a result is obtained through the synergic effect of several additives which are absorbed onto the surfaces of the aggregates.

The aggregates according to the invention are characterized as in claim 1.

According to one embodiment of the invention, the surfactant is preferably a synthetic anionic surfactant. It can, among other substances consist of at least one substance from the following list which should not be considered as limiting: - sodium abietate, - ethanolamine and triethanolamine salts, - fatty alcohol sulfonates, - alkylarylsulfonates, - sodium soaps of polyhydroxycarboxylic acids, - alkaline soaps of C12tc ^18 carb°n chain natural fatty acids, - surfactant derivatives of a protein nature based on animal blood.

This surfactant leads to air being released at the time the concrete is being mixed and contributes, firstly, to reducing the density of the concrete, an improvement in its compactness through the fine occluded air bubbles that play the role of a fine sand filling the interstitial spaces and, secondly, to a considerable improvement in the workability of the concrete right up to a point where it can be pumped. This amount of air is controlled both by the amount of make-water used and by the mixing time which is notably determined as a function of the speed of the mixing device.

In accordance with a further feature of the invention, the cement set accelerator is preferably sodium nitrate and/or chloride. It can also consist in at least one compound from the following list: - sodium chloride, - sodium or potassium hydroxide, Ϊ - alkaline-based salts such as carbonates, silicates, fluosilicates, aluminates, borates, * - calcium nitrite, - oxalic acid.

Any other known accelerator able to reinforce the early mechanical characteristics can be employed. In accordance with a further feature of the invention, the cement fluidifying agent is preferably a polynaphtalene sulfonate with 40% dry matter content or any other known agent for this application preferably having a high molecular weight, such as among other substances: - sodium lignosulfonate, calcium lignosulfonate, - formol melamin resin, - sodium abietate, potassium abietaie, - resin soaps.

The essential function of this agent is to improve the plasticity and mechanical characteristics of the concrete while simultaneously reducing the amount of make-up water.

The invention also describes a method for preparing aggregates the surface of which is coated by absorption of the specific mixture of the above-stated additives, according to which the aggregates are treated in the presence of this mixture of additives and of water in a blending device.

In accordance with one feature of the method of the invention, it consists in using for the treatment of 1 000 volumes of aggregate, a mixture of the three additives comprising surfactant, fluidifying agent and set accelerator in amounts of 1 000:1 000:4 000.

EXAMPLE 1 Preparation of an aggregate in accordance with the invention Vermiculite having the following characteristics was employed : . apparent bulk density ... about 60 kg/m^ . particle size ............ 6 to 1.4 mm The three additives were mixed in advance in a defined amount of water. Exfoliated vermiculite was introduced into the blending device through feed hopper 1 which sprayed it evenly over rotatable plate 3. This plate is perforated in order to increase the swirling motion of the particles that are already moving. The flow is then channeled by the fixed funnel-shaped member 4 prior to reaching spray chamber 5.

The liquid mixture of additives and water was fed under pressure through conduit 6 and sprayed through jet 8 into the heart of the fine descending swirling cloud of vermiculite. The swirling motion imparted to the particles particularly favours good contact between the sprayed liquid and the latter.

The surface-treated vermiculite was then collected in chamber 12 and supplied to the outlet opening 15 with the aid of a scraper 16.

The three additives were sprayed onto 1 000 liters of vermiculite in the following proportion: . anionic surfactant with 30% dry extract content .................................·.......... 1 000 1 . fluidifying agent (naphthalene sulfonate) with 40% dry extract content ................ 1 000 1 . set accelerator (sodium nitrate/sodium chloride in 50/50 weight percent proportion) ........ 4 000 g .water .................................... 34 000 g EXAMPLES 2 to 4 The thus-coated vermiculite was use in the preparation of concrete having the characteristics listed below.

Example 2 corresponds to a control using a vermiculite which had not been treated in accordance with the invention.

EXAMPLE 2 EXAMPLE 3 EXAMPLE 4 Composition per m3 of applied concrete Untreated vermiculite 1350 1 Cement CP 545 260 kg Make-up water - 370 kg Treated Vermiculite 1000 1 Cement CP 545 300 kg Make-up water - 240 kg Treated Vermiculite -1000 Cement CP 545 Make-up water - 220 kg Water/Cement ratio 1.42 0.800 1.1 Dry concrete density ~ 450 kg/m3 ~ 450 kg/m3 - 320 kg/m3 Workability dry concrete fluid concrete fluid concrete Appearance of concrete porous compact compact Compressive strength after 7 days 20°C - 50% RH ~ 0.4 MPa ~ 1 MPa ~ 0.4 MPa As can be seen from the table, the invention provides the advantage of making it possible, through the use of the thus-treated aggregates, lightweight concretes which were improved compared to those obtained using untreated vermiculate.

For equivalent densities, the amount of make-up water was reduced and the rheological characteristics of the fresh concrete together with the mechanical performance of the hardened concrete were distinctly better.

Claims

1. - Lightweight aggregate material with an increased density-reduction capacity for use in producing non-load-bearing lightweight concretes with a considerable water-absorption capacity, characterized in that the surface of said aggregates is coated with a mixture containing a surfactant, a cement set accelerator and a cement fluidifying agent, in that it has a density less than 1 and in that it is pre-calibrated by elimination of the fine fraction having a size less than 1.4 mm.

2. - Aggregate according to claim 1, characterized in that it consists of a material selected from the group schists and clays, and vermiculites, comprising expanded pozzolana, perlites polystyrenes, wood chips and cork.

3. - Aggregate according to claim 1 or 2, characterized in that it consists of vermiculite.

4. - Aggregate according to any one of claims 1 to 3, characterized in that the surfactant is a synthetic anionic surfactant.

5. - Aggregate according to any one of claims 1 to 4, characterized in that the cement set accelerator is sodium nitrate and/or chloride.

6. - Aggregate according to any one of claims 1 to 5, characterized in that the cement fluidifying agent is a polynaphtalene sulfonate with 40% dry extract content and high molecular weight.

7. - Aggregate according to any one of claims 1 to 6, characterized in that the volume ratio between the aggregate and the surfactant/fluidifying agent/set accelerator mass is about 1000 1/1000 g/1000 g/4000 g.

8. - Lightweight aggregate material with an increased densityreduction capacity for use in producing non-load bearing lightweight concretes with a considerable water-absorption capacity according to claim 1, substantially as herein described.