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Source/Context
The article contains a roughly translated summary and excerpts from the Scientific Report: V. Prikhodko and E. Kotlyarsk, “Construction of an experimental section of the foundation from the soil, strengthened with Portland cement using the additive Renolith on the educational and scientific base MADI (STU),” Ministry of Education and Science of the Russian Federation, Moscow, 2008
- Original language – German: Bau von einer Versuchsstrecke des Untergrundes aus dem mit Portlandzement verfestigten Boden, mit Einsatz von Renolith auf der Untersuchungsstation von MADI (STU)
- English, Machine translated by Google: Construction of a test section of the subsoil from the soil consolidated with Portland cement, using Renolith on the MADI Investigation Station (STU)
Overview
The investigation and construction work on pavement layers made of soil consolidated with Portland cement and Renolith additive was carried out in June-July of 2008 at the Institute for Automotive and Road Construction Moscow (MADI) State Technical University (STU) test field.
The objectives were:
- Approval of soil cement mix preparation technology with use of Renolith admixture on the mobile mixing plant “BERTOLI”;
- Determination of technological physico-mechanical properties of soil cement mix and soil cement in constructive layers of road beds.
Introduction
Because heavy transport in Russia and in neighboring countries continues to increase, it is necessary to adapt quickly to the growing volume of traffic and to expand the road network. This problem can be solved thanks to new technology, which can use the on-site soil for the road substructure and thus greatly reduce dependence on foreign materials in road construction. The use of soil stabilized with various binding materials is in ever wider use in road construction. The consolidation (stabilisation) of local soils allows a much greater range of usable materials in road construction. Recycling and use of local soil means reducing the materials to be delivered (e.g. gravel, coarse and small-grain sand); reducing the costs and transport impost for the construction of base layers in road construction.
The existing soils, with the addition of cement and special admixture (Renolith), can be used for the construction of the road substructure and achieve the necessary physical-mechanical properties (pressure and deformation resistance, frost resistance). High load capacity of the road substructure can be achieved. The biggest benefit of using this binder is that the mixtures can be prepared directly on site. Special mixing plants are required such as road milling machines and stationary mixing plants. Generally, such methods have application in the technical-economic effectiveness in road construction. However, traditional stabilisation construction methods have a number of significant disadvantages:
- Restricted use in road construction as not all soil types can be stabilized.
- The available material often has a high level of inhomogeneity and is therefore not suitable for traditional road construction.
- It is very challenging to stabilise soils with high water content and achieve the required carrying capacity.
- Asphalt laid on top of traditional base courses made with cement-only stabilised soils tend to form transverse cracks, leading to rapid destruction.
To improve the structural properties of soils solidified with cement, various additives are used here and abroad. Additives can make soils and aggregates hydrophobic and increase frost resistance of the material, or improve physical-chemical interactions with soil fines to form a denser and firmer material structure.
The additive to be examined – Renolith – can enable otherwise unsuitable soils to be utilised in road bases.
Test Field #1
The first test field was constructed on 05 June 2008. The composition of the solidified soil mixture was:
- Sand 100%
- Portland cement 8%
- Additive Renolith – 10% of cement mass
The sandy soil had a moisture content of 10%. 500 m3 of large grain sand was obtained from a pit near Moscow, bulk density 1.5 g/cm³.
Storage of the sand at the MADI test field
Portland cement brand 400 was made in Turkey and delivered in bulk bags. Because of improper storage and/or transport, the cement lost some effectiveness. Also, lumps had accumulated, causing partial malfunctions of the dosing device and affecting homogeneity of the mixtures.
The preparation of the above composition was made using a Bertoli brand mixer. This mixing plant has an output of 100 m³/h.
Bertoli mixing plant
The delivery of the mixture to the installation site was no more than 200 meters. Transportation was carried out using Kamaz trucks with a load capacity of 15 tons.
The application was done with the Vogele brand paver with a layer thickness of 18 cm installed.
Delivery of the cement soil mixture by truck and its unloading into the bunker of the brig. Application of the test section to the fire brigade aisle of the MADI test field
The pavement was compacted with a 12 ton two-roller vibrating roller brand DU 82 at a running speed of 1.3 km/h. 5-6 passes on each track were required to achieve full compaction.
Compaction of the mixture using a large roller
During the work process, the MADI specialist laboratory was used to determine the properties of the ingredients and mix. Reference samples were manufactured from 20kg of sand, 5kg of Portland cement and 2 litres of Renolith additive.
During the installation process, the layer density, layer thickness and width of the applied mixture was checked, as well as the number of rolling passes.
9 series of core samples (total of 63 cylinders) were drilled after 28 days cure.
Scheme of the test track on MADI test field with indication of the places where the cement soil mix samples were taken (9 places)
Laboratory tests were carried out in accordance with GOST 23558-94.
Test Field #2
The second test field was constructed on 15 June 2008. The technology for the construction of this road bed as well as the machines, mechanisms and soil mix were the same as for test field #1.
Core samples were taken from the installed base after 28 days curing. The sampling scheme for the core samples was similar to test field #1.
Sample core drilling
Drilled core sample
Control samples were prepared and stored for 28-days storage in a climate controlled chamber. The physico-mechanical properties of core samples the control samples were determined.
Tests
Tests were conducted on specimens and core samples to determine:
- Compressive strength
- Water absorption
- Relative deformation
- Flexural / tensile strength
Capillary water absorption test of the cement soil samples
Flexural strength test of 28d cured sample
Analysis
The ratio of compressive strength to bending strength to a certain extent characterizes the crack resistance of asphalt concrete pavements on soil bases reinforced with mineral binders. The ratios of compressive strength to bending (tensile) strength obtained from the results of testing samples and cores with 95% reliability lie in the range from 2.38 to 2.81. In accordance with the requirements of GOST 23558-94, these ratios should be no more than 5.00. The obtained ratios of compressive strength and tensile strength during bending suggest a higher crack resistance of soils reinforced with Portland cement and Renolith additive, which increases crack resistance of asphalt concrete pavements on cement-soil bases.
Water absorption of core samples selected from the base layer of the test site was determined in accordance with clause 6.1 of GOST 23558-94. To do this, the samples were placed in a bath filled with water at 1/3 of the cylinder height, and after 6 hours they were filled with water completely and kept for 42 hours. It is necessary to note the low values of water absorption, [the average values were between 0.75 and 1.09 M.-%], which creates the prerequisites for obtaining a material with high water and frost resistance.
Conclusions and suggestions
- Base mixes conforming to GOST 23558-94 brands M10 to M75 are possible using sandy soil with cement and Renolith additive:
- M10 (1MPa <= compressive strength <= 5.00* tensile strength)
- M75 (7.5MPa <= compressive strength <= 5.00*tensile strength)
- The water absorbency of the base courses is low. This means high water and frost resistance of these base layers.
- The use of “Bertoli” mixing plants enables mixing of the local soil in a timely manner. Because of the use of local materials and mixing plants, short transport routes are made possible. Transport costs are reduced enormously and pavement materials achieve a high load-bearing capacity.
- During the experimental and construction work, a non-homogeneous mixture of the cement base was noted. The causes can occur with continuous and flowing road construction and can be technically prevented. The causes were:
- Non-uniformity of materials used (variation of grit and moisture of the sand);
- Low quality of Portland cement made in Turkey and its activity losses during delivery and storage;
- Loss of dosing control during the preparation of the cement-soil mix through the mixing plant due to cement lumps;
- Insufficient quality of over-moist subsoil;
- We consider it expedient to evaluate the improvement of base layers achieved with Renolith in other soil types.
- It is necessary to add the additive Renolith to certify and to issue the certificate of conformity.
- It is necessary for the future to have a technology regulation for mixtures of cement bases with the additive for various types of road construction machines.
- The ratios of compressive to tensile strength allow higher crack resistance of Portland cement soil mixes with the additive Renolith. This reduces the risk of reflective cracking from the base layer to the asphalt layer.
- The road substructure can be made from local materials with the help of the hydraulic binders and use of the modern, efficient additive Renolith. Thus, the technological and structural properties of the road are easier to regulate. This allows for the construction of permanent base layers with the required transport and operational properties.