Scientific and technical goal of project "High-strength lightweight concrete" is creation of technology of high-quality building materials to increase efficiency of building and decreasing the cost of the specific area. Main task to achieve this goal is formulated: develope technology of new kind of concrete multifunctionaldestinationwitha universal set ofperformance properties.

Improving the quality of concrete as a most popular building material is a global trend which aimed to combine the positive attributes of light and heavy concretes. That is decreasing the average density and increasing the strength of concrete can to provide structural and heat insulating properties of these materials at the same time. But reduction the density of concrete less than 1800 kg/m³ leads to significant loss of strength and bearing capacity all in all.

Authors of this project developed technology of energy-efficient high-strength lightweight concrete (HSLWC) which has average density 1300-1500 kg/m³ and class of strength more than B45. Our concrete is almosttwice lighter and warmer than traditional heavy concrete, but it has the same high strength and freeze-thaw resistance (more than F300). Such properties are not possible for cellular concrete which are used today.

The high-strength lightweight concrete is fine-grained concrete which contains microscale spherical particles of filler. These microspheres together with special components of the cement-mineral composition and peculiar modifiers allow to form the dense and strong structure of the concrete with intense closed porosity at the same time.

The developed conrete is classified as material for construction with high operational properties. It can be used for building of multi-storey and high-rise buildings, railway and automobile bridges, overpasses, junction, manufacturing of big-span reinforced concrete products (girders, beams, crossbars, etc.) and other special difficult building objects.

Application of the high-strength lightweight concrete for construction allows:

• reduce the weight of the building and increase the maximum number of floors (up to 40%) due to low average density of concretes;
• reduce the requirements for the grounds and foundations and reduce the total cost of works at "zero cycle" 2-2.5 times;
• reduce the consumption of materials due to economy of concrete and metal reinforcement;
• improve the energy efficiency of the building during its operation (energy saving in heating);
• reduce the cost of transport and installation works in building process due to using the less lifting equipments;
• reduce the cost of one square meter of housing in high-rise building at 30%.
  
  Total efficiency of construction is increased at 30-35% due to application of high-strength lightweight concrete!

The composition and expense components of HSLWC are selected to ensure high strength of dispersed phase and dispersed medium and also high adhesion of the phase boundary. The main component for decreasing the average density is hollow glass and/or alumina-silicate microspheres. The frame-forming part contains four components different dispersion that allows to get high dense packing ofparticles, fillpores and achieve strong structure. The special bicomponent modifier grafted to the surface of the microspheres intensifies cement hydration and increases adhesion of the cement-mineral matrix to the particles of hollow filler.

The main properties of high-strength lightweight concrete

Table 1

Advantages of high-strength lightweight concretes

Concrete was and is main structural material for building of housing. The developed high-strength lightweight concrete has positive qualities and advantages in relation to traditional lightweight and heavy concretes (table 2). The low average density (almost 2 times) is the most important feature of HSLWC that is distinctive aspect from heavy concrete. Moreover the such concrete has high compressive strength (B30-B55) and high heat-conduction and temperature conductivity coefficients (more than 2.5 times).

The high-strength lightweight concrete combines high strength, low water adsorption and high freeze-thaw resistance in contrast tolightweight concretes. Homogeneous strong structure of HSLWC provides a mark of frost-resistance more than F300 (where total porosity is 33.4%) that is unattainable for traditional cellular concretes. Today the heavy and lightweight kinds of concretes are combined in building for structural and thermal-insulation functions. And properties of HSLWC allows to combine these functions in one material.

Table 2

Note: "+" is material has specified property; "–" is material has not specified property.

World analogues in the indicated direction

Developed composition of concrete exceed at 15-40% as compared with foreign analogues.

Table 3

Year	Country		Compressive strength, MPa	Average density, kg/m3	Specific strength, MPa
1999		Kuwait	22-25	1520-1550	14.4-15.0
2002		Germany	14-25	1800-1850	7.5-15.0
2003		Brasil	40-50	1450-1600	24.5-30.5
2003		Turkey	30-40	1800-1860	16.1-22.2
2004		Japan	47-54	1800-1850	27.5-30.0
2007		Russia	46-61	1800-1850	25.5-33.8
2007		Russia	42-48	1600-1650	25.4-28.7
2010		Malaysia	43-48	1870-1990	22.9-24.1
2011		Turkey	42-60	1840-1960	22.8-30.6
2012		Portugal	40-70	1500-2000	22.8-35.0
2012		HSLWC	40-70	1300-1500	30.0-50.0

Sphere of application of high-strength lightweight concrete

The energy-efficiency high-strength lightweight concretes can be used during the production of reinforced concrete

• for the industrial and civil construction of multi-storeyandhigh-rise residentialand public buildings,
• for the construction of automobile and rail bridges, overpassesandflyovers,
• for the manufactureof big-span reinforced concrete products (girders, beams, crossbars, etc.),
• other special difficult building objects.
  

An additional feature is the possibility of applying the such concrete for construction

• in difficult ground conditions (shorelineof rivers, lakes, seas),
• in areas with developedunderground communications (metro, tube, underground, tunnels),
• in seismicallyunstable regions.

Moreover, the application of HSLWC can be actual in other direction where it exposes to high requirements of operational properties for concrete or exists limit weight of products. For example, the production of warm facades, balconies, special material-storage with spherical shape, etc.

Technological scheme for plant of reinforced concrete products

Materials and composition (recipe) of high-strength lightweight concrete

The high-strength lightweight concrete is made of concrete mixture of special composition. It consists of cement, filler (microsphere) desired size, quartz sand, plasticizer and water. The mandatory part is mineral components included siliceous modifiers defined composition and granulometry. The effective plasticizers for these mixtures are polycarboxylate additives. HSLWC does not include a coarse aggregate. The special composition of HSLWC allows to provide the forming of dense and strength structure together with saturated closed porosity.

The cement CEM-I 42.5 N is used for preparation of developed concrete. The mineral part permorms the function of the packing to increase the density of concrete. Quartz sand has fraction 0.16-0.63 mm. The application of polycarboxylate additives (Sika, Melflux, Odolit-T and other) allows to increase the mobility and decrease the water demand of the concrete mixture. 

The important component for HSLWC with special operational properties is unique nanosized modifier which is developed in sientific center "Nanomaterials and nanotecnology" (MSUCE) and is used for modification of the surface of filler parts. It interacts with cement and hydration products to increase the adhesion of contact zone of the spherical parts and frame-forming components of HSLWC.

The quality of HSLWC products depends of prescription and tecnological factors: preparation and laying modes, mode of heat and humidity treatment and other.