Grout for making watertight screens

Abstract

The invention relates to a grout for making watertight screens which comprises a mixture of water, natural or modified clay, specific blast furnace slag and an activating agent.

Description

The present invention relates to the field of construction and building. More specifically, the invention relates to a grout for making watertight screens, as well as to a process which makes use of said grout.

It is known that ground blast furnace slag behaves as a real cement when a base such as sodium hydroxide or clinker for example is added thereto.

Thus, usually, mixtures of the following types are found on the market:

• • slag+clinker in well defined proportions (Cement CLK CEM III/C, CHF CEM III/A or B), or
  • granulated slag+lime, intended for road works.

Making watertight screens is done by direct perforation with bentonite cement grout as excavation fluid. The perforation is done continuously from which comes the necessity of having a material which does not harden too quickly so as to prevent losses of grout on the excavation cuttings as well as the evacuation of grout which might have hardened prematurely. This specific method for watertight screens necessitates, with the materials which are currently available, the use of setting retarders and hardening retarders.

A good watertightness is in fact sought after during the making of watertight screens. The resistance is in general low and does not represent an essential criterion. In general, slag cements are used the composition of which generates grouts the rheology of which is difficult to control. The use of retarder additives is thus necessary to obtain a manoeuvrability which is compatible with the perforation with a grout.

The aim of the invention is to remedy these drawbacks. Thus, the objective of the invention is grouts which are particularly adapted to the making of watertight screens, in particular grouts which do not necessitate the addition of retarders.

Thus, the invention relates to a grout for making watertight screens which comprises a mixture of water, a natural clay or a modified clay such as bentonite, a blast furnace slag and an activating agent.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows the evolution of the permeability as a function of the cement/water ratio.

In accordance with the invention, said slag comprises grains the maximum size of which is between about 50 μm and about 100 μm, preferably equal to about 80 μm. The slag preferably has a Blaine specific surface area of about 2,500 to about 4,500 cm²/g.

Although the nature of the blast furnace slag is not particularly critical, it is preferable that it be of the basic type and that the CaO/SiO₂ weight ratio be between about 1.10 and about 1.35. A material which comprises 33 to 40% SiO₂, 8 to 16% Al₂O₃, 39 to 44% CaO, and 4 to 9% MgO (in percentages by weight) as main components can be cited as an example of a slag which can be used within the context of the present invention.

Furthermore, it is also preferable that the chemical modulus of the slag (CaO content (%)×Al₂O₃ content (%)) be greater than about 500.

The activating agent enables the setting of the slag and is preferably a basic activating agent such as sodium hydroxide, potassium hydroxide, sodium or potassium (bi)carbonate, gypsum, quicklime, slaked lime or a mixture of these compounds. It is also possible to use Portland cement as activating agent.

In general, the amount of activating agent is between about 1% and about 10% by weight, with respect to the weight of the slag. An amount of activating agent equal to about 5% by weight is particularly advantageous.

Advantageously, such a grout has a cement/water weight ratio (C/W) of between about 0.1 and about 0.25.

Under these circumstances, it is possible to obtain a grout having the following properties:

• • a greater resistance for a same cement/water ratio,
  • a better permeability at an equivalent dry matter content (as FIG. 1 shows, which represents the evolution of the permeability as a function of the C/W ratio), and
  • a very slow evolution of the rigidity which is well adapted to the direct perforation with a grout. The low reactivity of the system makes it possible to totally do without the use of retarders. The suppression of such additives enables the ground water to be respected by eliminating organic pollutant waste.

This grout can be used for underground work in contact with the ground water by virtue of its non-pollutant character, and it can be used for injection works and in the making of plastic concrete watertight screens.

The grout is prepared on the drilling site by mixing the components defined supra.

The invention will be better understood with the aid of the following Examples, which are given in a purely illustrative manner.

The following constituents are used in these Examples:

• • bentonite slurry: mixture of 1,000 l of water and 45 kg of sodic bentonite
  • slag: basic blast furnace slag having a CaO/SiO₂ weight ratio equal to 1.19 and a chemical modulus equal to 515
  • activating agent: CPA CEM I
  • retarder: mixed calcium/ammonium lignosulphate
  • accelerator: sodium silicate 35/37 °B

EXAMPLE 1

Influence of the Maximum Grain Size of the Slag Upon the Manoeuvrability Time of the Grout

Grout	Slag 40 μm	Slag 80 μm	Slag 120 μm
manoeuvrability	5 hours	5 hours	5 hours
time
Bentonite slurry	941 l	941 l	941 l
Slag	166.25 kg	166.25 kg	166.25 kg
Activating agent	8.75 kg	8.75 kg	8.75 kg
Retarder	3 l	0	0
accelerator	0	0	4 l

EXAMPLE 2

Formulations for Watertight Wall

	invention	comparative
	Bentonite slurry	941 l	941 l
	Slag*	166 kg
	Activator (CPA CEM I)	9 kg
	CLK		175 kg
	Retarder		2 l
	Manoeuvrability time	5 h	5 h
	Resistance 28 days	1.2 MPa	1 MPa
	Permeability	5 10−10 m/s	4 10−9 m/s
	*the slag has a continuous particle size ranging from 0 to 80 μm and a Blaine specific surface area equal to 4500

The grout in accordance with the invention, without retarder, has a manoeuvrability time which is identical to conventional grout comprising clinker (CLK) and a retarder, as well as a better resistance and a better permeability than conventional grout.

Claims

1. A grout for watertight screens, which consists of water, a natural or modified clay, a blast furnace slag having a maximum grain size of between about 50 μm and about 100 μm and a Portland cement as an activating agent, wherein said grout has a cement/water ratio of between 0.1 and 0.25.

2. The grout according to claim 1, in which the slag has a maximum grain size equal to about 80 μm.

3. The grout according to claim 1, in which the slag has a CaO/SiO2 weight ratio of between 1.10 and 1.35.

4. The grout according to claim 1, in which the slag has a chemical modulus of greater than about 500.

5. The grout according to claim 1, in which the modified clay is bentonite.

6. The grout according to claim 1, in which the amount of Portland cement is about 1% to about 10% by weight with respect to the weight of the blast furnace slag.

7. The grout of claim 1, in which the slag has a Blaine specific surface area of about 2,500 to about 4,500 cm2/g.