MXPA00007982A - Chemical agent for improving the engineering properties of soil - Google Patents

Abstract

A chemical agent for improving the engineering properties of soil comprising a mixture of cementitious pozzalans (5 to 60%by mass), calcium sulphate (20 to 80%by mass), an oxide of calcium (15 to 50%by mass) and silica oxide (1 to 30%by weight). Monofilament fibres can also be included in the mix.

Description

CHEMICAL AGENT TO IMPROVE SOIL ENGINEERING PROPERTIES FIELD OF THE INVENTION This invention relates to a chemical agent for improving the engineering properties of the soil.

BACKGROUND OF THE INVENTION In many civil engineering situations it is essential that in situ soil has its improved engineering properties before being used in construction work. This is particularly important in road construction where adequate failure to stabilize the underlying soil can result in the road sinking and / or cracking in use. The simplest way to overcome the properties of the soil is to compact it. However, because soils vary from sandy material to clayey material, compacting the soil simply does not necessarily improve its engineering properties sufficiently to support anything that is built on it. As a result of this it has been proposed to incorporate chemical agents in the soil to improve it and many polymer-based stabilizers have been used. These are successful in improving soil properties, but only for a relatively short period of time. Eventually, the polymer leaches from the soil and its effect is lost. While the chemical agent of the present invention is specifically designed to stabilize the area to be supported by a construction, it can also be mixed with soil and the resulting mixture pressed into molds to form building elements, for the construction of low housing. cost.

BRIEF DESCRIPTION OF THE INVENTION According to the present invention, a chemical agent is provided to improve the engineering properties of the soil, the agent comprises: between 5 and 60% by mass of a cementitious pozzolan; between 20 and 80% by mass of calcium sulfate; and between 15 and 50% by mass of a calcium oxide.

It is preferred that the chemical agent for the improvement of soil properties comprises: between 15 and 35% by mass of a cementitious pozzolan; between 40 and 60% by mass of calcium sulfate; and between 20 and 40% by mass of a calcium oxide. In a further preferred form the chemical agent comprises: between 25 and 30% by mass of a cementitious pozzolan; between 30 and 40% by mass of calcium sulfate; and between 25 and 35% by mass of a calcium oxide. The preferred pozzolan is blast furnace slag mixed with ordinary Portland cement, preferably in equal masses. Blast furnace slag is generally referred to as slag. The chemical agent may also include additional pozzolanas selected from ordinary Portland cement (referred to in the industry as OPC), sulphate-resistant cement, Portland cement 15 SL, Portland cement 15 FA, mixtures of ordinary Portland cement and ash dust, and cement from masonry. The chemical agent can include reinforcing fibers such as fibers of a synthetic plastic material. Preferred fibers are polypropylene monofilaments. Between 1 kilogram and 10 kilograms of fibers can be added to every 100 kilograms of chemical agent. The calcium oxide can be in the form of calcium oxide (CaO) or calcium hydroxide (Ca (OH) 2). Calcium sulfate can be mineral gypsum or partially dehydrated gypsum (CaS04 »^ H20) In one form the chemical agent includes 1 to 30% by mass of silicon oxide (Si02). A specific form of chemical agent that is particularly suitable for use in improving the properties of a road surface comprises: Mineral gypsum (CaS04) 35% by mass Quartz sand 12% by mass Calcium oxide or calcium hydroxide 25% by mass Portland cement blast furnace 28% by mass According to a further aspect of the present invention, a method is provided for improving engineering properties in the soil, which comprises scarifying or de-soiling the soil to break up and pulverize the soil, applying the chemical agent described above on the ground, mixing the soil and the chemical agent, and then compacting the soil. According to a further aspect of the present invention, there is provided a method for manufacturing building blocks from the soil comprising breaking the soil, mixing it with the chemical agent, compacting the soil of the chemical agent mixed into a mold and leaving that the mixed soil and chemical agent settle and harden.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE 1 The chemical agent according to the present invention can be used, in the manner to be described, to improve the soil properties of a road with gravel or powder to be concreted, tarred (smeared with tar), concreted with brick or sealed with a bituminous surface seal. The road can, however, after improvement, be used without tarmac or concretion, the improved soil forming the surface on which the traffic flows. The existing gravel road or road is scarified to the depth at which stabilization is required. The scarification breaks and pulverizes the existing superficial layer of the road after which the soil in situ is perfectly mixed by means of a leveling machine or rotovapor (rotary cultivator). A chemical agent having the following constituents is then spread as a layer on the scarified surface, at the predetermined dose which has been determined by laboratory tests. Such tests are described hereinafter with reference to Examples 2 etc .: Mineral gypsum (CaS0) 35% by mass Quartz sand 12% by mass Calcium oxide (CaO) or 25% by mass calcium hydroxide (Ca (OH) 2) Portland cement blast furnace 28% by mass The mineral gypsum and the quartz sand are available pre-mixed. The mixture is sold under the trade name "Cretestone". The total amount of Cretestone used is 47% by mass. The portland blast furnace cement comprises slag (the residue from blast furnaces) that is crushed and mixed with an equal mass of OPC (ordinary Portland cement). One kilogram of reinforcing fibers can be added per one hundred kilograms of the previous mixture. Other products that can be used are CB Plaster and Hydrostone, each of which contains mineral gypsum and quartz sand. The amount of agent applied varies with the nature of the soil type and also as a function of the most economical dose for the type of soil, but is generally in the range of 2% to 10% by mass of the soil that is going to be improved. The chemical agent is then perfectly mixed in the scarified layer until a homogeneous layer has been obtained. Experimental work has shown that a rotovapor intimately mixes the chemical agent with the soil in a more satisfactory way. Water is then added and mixed until uniformly distributed throughout the mix and until the OMC (optimum moisture content) of the stabilized soil has been reached, as determined in the laboratory beforehand.

The stabilized layer is then compacted using road compactors until the specified density of the layer has been achieved. Finally, the stabilized layer is leveled to the final level of the road and compacted until a smooth surface layer has been obtained. Experimental work has shown that the chemical agent used does not leach into the soil after the agent has hardened.

EXAMPLE 2 A soil was tested in Malaysia. The soil was a muddy (clayey) sand that was classified as A 2-6. This was tested using the standard unconfined compression strength tests (UCS) and the California Load Support Ratio (CBR). The chemical agent used was that described in Example 1. The soil sample had the following characteristics: plasticity index 12 (on the material <0.425 mm) MDD (maximum dry density) 2039 Kg / m3 OMC (optimum moisture content) 9.2% UCS Test Results CBR Test Results From this test it can be concluded that the resistance of the treated material increased between 3 and 4 times with respect to the original strength.

EXAMPLE 3 Two samples were tested in Israel by the Israel Standards Institute. Sample 1 was a stony gravel of soft limestone. The sample 2 comprised green carbonated clay. Table 1 gives the properties of the two samples. The tests were carried out on sample cylinders with a diameter of 35 mm and a width of 80 mm. The measurements and method of sample preparation were chosen according to ASTMD standard 2850-87 of "Standard Test Method for Unpressurized, Unconsolidated Compression Resistance of Cohesive Soils in Triaxial Compression". Graphs 1 and 2 show the influence of the chemical agent of Example 1 on the strength of samples 1 and 2, respectively. Graphs 3 and 4 show the results of the CBR tests on samples 1 and 2. It will be noted that with increasing percentages of the chemical agent according to the present invention, the properties of the samples are greatly improved. The term RBI means a chemical agent having the composition described in Example 1.

EXAMPLE 4 If it is used in the production of construction elements such as bricks or blocks, the chemical agent of Example 1 is mixed with soil. For example, it can be mixed with the soil that is removed to form the foundation of a building. The mixture is then placed in molds and compacted in the molds. Once the mixture has hardened sufficiently, the building element is removed from the mold and allowed to harden before being used for construction purposes.

EXAMPLE 5 It was tested a gravel from Sri Lanka that has the following properties.

After mixing the sample with 6% by mass of the chemical agent of Example 1, the following results of the CBR test were obtained.

It can be deduced that the CBR value at the standard density of 100% has increased significantly from a value of 24 to 213, for example, between 8 and 9 times when stabilized with 6% of the chemical agent compared to the CBR value not stabilized This indicates that there is a significant increase in CBR resistance when stabilized with the chemical agent.

EXAMPLE 6 A muddy, clayey sand, with gravel dispersed in it and having the following properties, was used in this test: The soil was classified, according to the AASHTO classification, as A.l-b. The chemical agent mixed with the soil for testing purposes had the following composition: Plaster (CaS04) 33% by mass Limestone (not crumbled) CaO 27% by mass OPC / slag 27% by mass Quartz sand 13% by mass The following results were obtained by the CBR test: The resistance to support soil load increased significantly. The maintenance of the treated road decreased significantly.

There was less bump formation and loss of gravel from the surface during humid weather.

EXAMPLE 7 A sample of gravel from brown granite was obtained from a highway in the province of KwaZulu Natal. The sample had the following properties and was again classified as A.l-b: The composition of the chemical agent used was as follows: CB plaster (CaS04) 60% by mass Hydrated limestone (Ca (OH) 2) 15% by mass Slag / OPC in equal amounts 27% by mass The following results were obtained from the CBR test: The CBR of the load resistance of the treated sample increased dramatically with respect to the untreated sample. The final product was hard and could serve well as a road surface. However, this was not durable as the applicant desired, and the high percentage of expensive gypsum made the product too expensive for general use. The chemical agent could be very well used where the treated soil is a sub-layer that is covered by bitumen, concrete, etc.

EXAMPLE 7 An aggregate of crushed stone plus soil, believed to be of sandstone or granite origin, was taken from a secondary road in a housing area. The road showed potholes, corrugations and erosion due to inadequate drainage of surface water. The AASHTO classification was again A.l-b. The properties of the soil were as follows: The composition of the agent used to treat the sample was as follows: Gypsum (CaS04) 60% by mass Limestone (Ca (OH) 2) 20% by mass Slag / OPC 20% by mass It will be noted that the agent did not include quartz sand. The resulting surface of the road was hard and durable, but the product was too expensive for general use due to the high gypsum content.

EXAMPLE 7 Tests were carried out in a fine sand classified as A.3. The chemical composition of the agent used was as follows: Plaster (CaS04) 45% by mass Limestone (Ca (0H) 2) 50% by mass Cement (OPC) and blast furnace slag 5% mass The CBR test gave the sand, before treatment, a reading of 30 and to the sand after treatment with 5% by mass of the chemical agent a reading of 178. The final product, however, broke when excessive pressure was exerted over it while passing traffic. In this way, it is too weak for use with a surface layer, but suitable for use as a sub-layer in areas that do not carry heavy loads. Soils, whether sandy or clayey, respond to treatment with a mixture of pozzolan, calcium sulfate and calcium oxide, and show improved CBR values. Some chemical agents, in accordance with the present invention, particularly those that utilize a high percentage of calcium sulfate, are too expensive for general purpose use, to improve the engineering properties of the soil that is to become an upper layer or a sub-layer of a highway. However, these are usable to treat smaller areas where substantial improvement in properties is required. Other chemical agents improve CBR values but the treated soil is less durable than necessary for a road surface. Soils treated with these agents are suitable as sub-layers on which a layer of brick, concrete, bitumen, etc. is applied. To produce the chemical agent, the required amounts of CaO and CaS04 are weighed and mixed until the mixture is homogeneous. The required amount of quartz sand is then mixed until the mixture is homogeneous. Finally, the cementitious pozzolana is mixed in the mixture of CaO, CaS04 and quartz sand. Different types of limestone can be used. The following are examples: The magnesium content should be less than 5% by mass and the ratio of calcium oxide to magnesium oxide should be greater than 14 to 1.

Claims (12)

1. Method to improve the engineering properties of the soil, which includes scarifying or debranching the soil to break up and pulverize the soil, applying to the soil a chemical agent comprising: between 5 and 60% by mass of a cementitious pozzolana; between 20 and 80% by mass of calcium sulfate; and between 15 and 50% by mass of a calcium oxide, mixed the soil and the chemical agent, and after that compact the soil.

2. Method of manufacturing building blocks from the ground comprising breaking the soil, mixing it with the chemical agent comprising: between 5 and 60% by mass of a cementitious pozzolana; between 20 and 80% by mass of calcium sulfate; and between 15 and 50% by mass of a calcium oxide, compacting the soil and chemical agent mixed into molds and letting the mixed soil and chemical agent settle and harden.

3. Method according to claim 1 or 2, wherein the agent comprises: between 15 and 35% by mass of a cementitious pozzolana; between 40 and 60% by mass of calcium sulfate; and between 20 and 40% by mass of a calcium oxide.

4. Method according to claim 1 or 2, wherein the agent comprises: between 25 and 30% by mass of a cementitious pozzolan; between 30 and 40% by mass of calcium sulfate; and between 25 and 35% by mass of a calcium oxide.

5. Method according to any of claims 1 to 4, wherein the pozzolan includes blast furnace slag cement.

6. Method according to claim 5, wherein the chemical agent also includes additional pozzolans selected from cement Ordinary portland, mineral gypsum and partially dehydrated gypsum.

7. Method according to claim 5 or 6, wherein the chemical agent comprises equal masses of blast furnace slag cement and ordinary Portland cement.

8. Method according to any preceding claim, and including the step of mixing reinforcing fibers with the chemical agent.

9. Method according to claim 8, wherein the fibers are of a synthetic plastic material.

10. Method according to claim 8 or 9, wherein between 1 kilogram and 10 kilograms of the fibers are added per 100 kilograms of chemical agent.

11. Method according to any preceding claim, wherein the calcium oxide is in the form of calcium oxide (CaO) or calcium hydroxide (Ca (0H) 2).

12. Method according to any preceding claim, and including 1 to 30% by mass of silica oxide.