ADING in Kazakhstan – construction of motorways with cement-concrete pavements
In 2007 Kazakhstan launched a grandiose undertaking for reconstruction and building of the infrastructure network of the country. The initial emphasis was on the motorway network which should provide efficient link between 14 regional centres of the country. After the successful construction of the first experimental motorway section of cement concrete pavement from Astana towards Petropavlovsk, a strategic decision was made that all new motorways should be constructed as cement concrete pavements. This investment is, of course, around 30% more expensive than roads built in the form of asphalt concrete pavements; however, it is more favourable to the local climate conditions and further maintenance.
The year 2010 marked the beginning of the construction works on the transit corridor “Western China – Western Europe” through Kazakhstan, also known as “the silk road”. From Horgos at the border with China all the way to the border with Russia, the route extends to a length of 2,787 km. The construction activities on the sections Astana-South (towards Karaganda and Almaty) and Astana-East (towards Pavlodar) began in 2012 and 2013, whereas the preparations for the construction activities at the section Astana-West (towards Aktau), which also measures thousands of kilometres in length, are underway. These are impressive financial and construction undertakings which involve domestic and international construction companies.
In 2008, the company ADING through its affiliate in the city of Almaty joined the project, i.e. the 57 km long section Astana-Shchuchinsk, where ADING’s concrete admixtures were applied and professionals from the company were involved in the construction activities. Following its success in the first project, the company became part of numerous projects for construction of concrete motorways in the vast territories of Kazakhstan. The Macedonian company was working side by side with other national and international companies from Turkey, Azerbaijan, Italy, Germany, Iran, etc., on the construction of the sections: Taraz – border of the South Kazakhstan Region, ring road of the city of Shymkent, entrance section to the city of Turkistan, the section Astana – Karaganda, two sections Almaty – Kapchagay, the section Astana – Pavlodar, etc.
The modern technology for construction of motorways with finishing cement concrete pavements implies the use of state-of-the-art technology for that purpose. With powerful construction machinery, under tight deadlines, the trenches were filled with materials that measure in millions of cubic metres, hundreds of thousands cubic metres of stabilised subgrade and subbase of natural gravel, tens of thousands of cubic metres of cement stabilised base layer and hundreds of thousands of cubic metres of cement concrete pavement successfully installed.
The concrete batching plants have a production capacity of 240 m3 of concrete per hour. The recipe for concrete, apart from the standard ingredients: sand, gravel, cement and water, must include concrete admixtures which enable the concrete to meet the required features for this type of concrete. Certain conditions must be met, such as: delayed initial set of the concrete mix because of the long transport with dumper trucks, better placeability of the concrete which has very low water-cement ratio (w/c ratio = 0.36 – 0.39), controlled setting of the placed concrete, ice resistance, high initial and final strength, etc. For achieving the planned properties of the concrete, several products from the product range of ADING were used, including the admixtures SUPERFLUID-M1 and POROCINITEL and materials for protection of freshly poured concrete, the paraffin wax-based curing compound ZASTITA-B and the acrylate-based curing compound ZASTITA-B3.
The concrete finishing machines that are used for placing the concrete are also the latest achievement in the field of mechanical engineering. These machines which can weigh up to 140 tonnes and which also integrate the electronics can place the delivered concrete in the form of cement-concrete pavements measuring 16 m in width and 40 cm in depth. The pavements built in Kazakhstan are without reinforcement and measure 9.25 m, 11.00 m, 13.50 m and 14.75 m in width and 25-28 cm in depth, depending on the planned road load and amount of traffic. Unlike the old technology for construction of cement-concrete pavements that involved placement of the concrete in stages in the form of independent, but mutually connected concrete blocks, the new technology involves placement of the concrete in a uniform and continuous procedure. The later free expansion of the cement-concrete pavements due to temperature changes and variations is enabled by creating joints by cutting the concrete at precisely determined positions. This time, we will pay special attention to the joints which are a very important element in the construction of pavements.
Depending on the temperature and weather conditions, the cutting of concrete begins two or more hours after it has been placed. Transverse joints are cut to a depth measuring 30-40% of the thickness of the concrete at a distance of 5 m, exactly on the middle [at an equal distance] between the joints that have already been installed, whereas the longitudinal joints are cut to a depth of 40-45% of the thickness of the concrete, at an equal distance from the installed anchors: one pavement joint measuring 10 m in width, two pavement joints measuring 13.5 m in width and three pavement joints measuring more than 13.5 m in width. When determining the position of the joints, efforts should be made to form a field with an approximate square shape covering an area not larger than 30 m2. Also, when positioning the longitudinal joints, they should not overlap with the line of movement of the tyres of vehicles driving on the pavement.
The joints and anchors are planted into the freshly placed concrete by using a mechanism that is incorporated into the concrete finishing machine to a depth that is exactly at the middle of the layer of the concrete pavement. The joints are made of smooth steel and are entirely covered with a coating of synthetic paint measuring 0.3 mm in thickness, or they are wrapped in PE foil in order to prevent that the concrete comes into contact with the steel. The anchors are made of ribbed steel bars and are partially coated at the centre as a precaution against corrosion in the event of accidental penetration of water through the joint. In fact, the joints lay freely in the pavement, whereas the anchors should establish a very strong bond with the concrete. The role of the joints is to absorb the load [expansion and contraction] which occurs as a result of the discontinued concrete pavement due to the positions cut for installation of the joints, thus preventing differences in the elevation of the formed concrete blocks. The dimensions of the joints and the distance between them which ranges between 25 and 50 cm, depends on the estimated load. The ribbed steel anchors, apart from absorbing the load, they ensure and prevent the mutual separation of the concrete blocks. They are placed at distance from each other between 1.0 and 1.2 m.
The creation of the joints involves several stages. The first stage is the cutting of the concrete, i.e. to make a cut to the already indicated depth that will be 4 mm wide. Later the cut enables the concrete to continue with the controlled cracking along the entire transverse cut, thus creating concrete blocks that can freely expand under load, but which are fully integrated in the pavement and connected with joints and anchors.
At the next stage, after the seventh day of concrete curing, cuts are made that are 8 mm wide and 3.5 mm deep towards the interior of the joint and then it is followed by a process of chamfering, i.e. chamfering the edges of the joints on the surface of the concrete. Following the full curing period of concrete, i.e. after 28 days, when concrete humidity falls below 5%, the joints should be hermetically sealed according to the following procedure: the joints should be cleaned and dusted by applying compressed air. They should be primed with the primer BITEK-P in order to ensure strong adhesion between the concrete and the sealant used for grouting the joints. Neoprene tubing is installed in the joints in order to prevent the uncontrolled outflow of excess sealant. In the end, the sealant BITEK-A is applied. It is a hot-applied sealant which ensures complete sealing of the joint. The hermetic sealing of the joint prevents the penetration of water and the negative impact of potential ice inside the joint on the uniformity of the concrete structure.
Quality construction of cement-concrete pavements requires extensive knowledge of concrete as a building material, high level of training for use of the modern machinery, as well as compliance with the technology rules for this type of construction activities.