Portland Cement CEM Research Articles

Durability of Fly Ash Eco-friendly Cement Mortars in Severe Environment

The incorporation of waste and industrial by-products into concrete has been one of the alternatives to reduce the world consumption of cement and, consequently, to make it a more eco-friendly material. Therefore, and knowing that durability plays an important role in the life cycle of the construction materials, this work investigates the durability of cementitious materials with incorporation of fly ash (FA) when submitted to environments containing simultaneously the aggressive agents Cl- and CO2.The increase in the amount of aluminates provided by cement substitution by FA is one of the factors that leads to a decrease in the free chlorides content since the aluminates react chemically with the chlorides binding them. On the other hand, Ca(OH)2 present in the matrix from cement hydration is consumed due to the pozzolanic reactions, facilitating the advance of the carbonation front. In this context, it is important to know the behaviour of cementitious materials containing FA in environments subjected simultaneously to chlorides and carbonation.Mortar specimens containing 0, 20, 40 and 60 %wt of Portland cement CEM I 42.5R replaced by FA were moulded. After 90 days of curing, half of the specimens were introduced into the carbonation chamber (20 ºC, 55 % RH and 4 % CO2) where they remained for 15, 60 and 90 days. The other half was protected with plastic film during the same period. After, the specimens were subjected to the chloride diffusion test by migration.According to the obtained results, there was an increase in the chloride diffusion coefficient of the mortars submitted to the combined action for all percentages of FA incorporation. However, this increase was most evident for the higher percentages of cement replaced by FA. This fact may be related to the increase in the large capillary pores caused by carbonation and to the fact that the carbonated concrete has its chlorides binding capacity reduced.

PHYSICAL AND MECHANICAL PROPERTIES RESEARCH AND ANALYSIS OF CONCRETE WITH BIOFUEL COMBUSTION FLY ASH SUPPLEMENT

Materials used for the study: Portland cement CEM I 42,5 R, 0/4 fraction sand, 4/16 fraction gravel, biofuel fly ash, superplastizer ViscoCrete D187 (V) and water. Seven compositions of concrete were designed by replacing 0%, 5%, 10%, 15%, 20%, 25% and 30% of cement with biofuel fly ash. The article analyses the effect of biofuel fly ash content on the properties of concrete. Studies have shown that the increase of biofuel fly ash content up to 15% increases concrete density and compressive strengh after 28 days of curing, compressive strength, ultrasonic pulse velocity, closed porosity, concrete forecasted freeze-thaw cycles and decreases water absorbtion, open porosity.

The Influence of a Polymer Powder on the Properties of a Cold-Recycled Mixture with Foamed Bitumen.

The paper investigates the influence of redispersible polymer powder (RPP) on the physical and mechanical properties of a cold-recycled mixture with foamed bitumen (CRM-FB). Four types of RPP with a varied chemical base were used: VA-VeoVA, VA-VeoVa-Ac, EVA and VA/VV/E/Ac. The polymer powder-modified cold recycled mixture with foamed bitumen, (P)CRM-FB, was composed of 45.8% reclaimed asphalt pavement (RAP), 45.8% natural aggregate (VA), 3.0% Portland cement CEM I 42,5R, 3.0% foamed bitumen 50/70 and 3.0% RPP, all dosed by weight. The reference mixture, (R)CRM-FB, served as a reference point for comparison. It was found that RPP improved the workability of the CRM-FB mixture. This results in a reduced number of compaction cycles and lower energy needed to obtain the air void content as in the reference mixture. In addition, the RPP modifier markedly increased the CRM-FB mixture cohesion (ITSDRY) and strength, by approximately 40–70%, depending on the RPP used. These findings are particularly important for CRM-FB mixtures designed for road bases. The present investigations confirmed the improvement of the CRM-FB mixture parameters after the modification with RPP, regardless of the powder type used.

Life cycle assessment of the use of sewage sludge as Portland cement replacement

In this paper, we proposed an alternative thermal treatment of sewage sludge, aimed at its application in blended cements, which can reduce the energy demands and requires less technologically sophisticated processing. The life cycle assessment (LCA) was performed to quantify the environmental impact of the sewage sludge used as a partial cement replacement. The LCA was focused on the CO2 emission and energy consumption. The functional unit of 1 m3 of blended mortars composed of Portland cement CEM I 42.5, silica sand, and thermally treated sewage sludge, where the sludge was used as partial cement substitute in a dosage of 10, 20, and 30% by mass of cement, was analyzed. The positive effect of the use of sewage sludge as a partial cement replacement with respect to the energy consumption and GHG emission, considering the compressive strength of the analyzed composites, was quite apparent. The decrease of energy consumption necessary for the production of the analyzed blended binders was nearly 10% per each 10% of sewage sludge used as Portland cement replacement. The energy needed for the sludge thermal treatment at 700°C was 220 MJ/t. The emission of GHG related to the sludge thermal treatment was 40kg/t. The presented data were strongly affected by the applied distribution of electricity sources, with a high share of coal combustion plants.

Development of nanomodified rapid hardening clinker-efficient concretes based on composite Portland cements

It has been shown that significant reduction of «carbon trace» in construction technology is achieved by production of clinker-effective concretes based on composite Portland cements. Studies have shown that uneven distribution of grain fractions of the filler mix and their increased specific surface area lead to growth of water demand, stratification, bleeding in the concrete mix and a decrease in concrete strength. To achieve higher grain packing density, an approach based on optimizing particle size distribution in the concrete mix components was implemented. It was found that increased early strength of concretes based on low-emission composite cements is achieved by introduction of polycarboxylate (PCE) superplasticizers and alkaline-sulfate activation. To establish connection between environmental and technical properties of concretes, clinker efficiency in concrete was determined. An increase in strength of modified concrete based on composite Portland cement CEM II/B-M 32.5 R (clinker factor 0.65) create the possibility for a significant reduction of specific consumption of clinker per unit strength, up to 4.5…3.0 kg/(m 3 MPa); accordingly, CO 2 intensity 3.9...2.6 kg CO 2 /(m 3 MPa). Significant intensification of the processes of early structure formation in nanomodified clinker-efficient concretes is ensured by a comprehensive approach: optimization of the component mix, introduction of the PCE superplasticizer and nanomodifiers. Using the laser diffraction method, it was proved that main contribution to development of specific surface of the nanomodified cementing matrix is made by ultrathin particles ( K isa =761.2 μm –1 vol. %) of nano-SiO 2 . It was established that synergistic combination of mineral additives in composite Portland cement and complex nano-SiO 2 +C-S-H-PCE nanomodifier provide increased early strength (after 12 hours – R c =6.4 MPa) and obtaining rapid hardening concrete class C50/60 ( f cm 2 / f cm 28 =0.51). Thus, there are reasons to argue that it is advisable to develop nanomodified clinker-efficient concretes in order to ensure rapid construction and solve problems connected with necessity of implementation of a strategy of low-carbon development

Quality of water recovered by treating acid mine drainage using pervious concrete adsorbent

In this paper, a batch experiment was conducted to evaluate the water quality obtained from using pervious concrete (PERVC) technology to treat acid mine drainage (AMD). The study proposes an innovative application of PERVC as a permeable reactive barrier liner in evaporation ponds. The effectiveness of PERVC adsorbent in removing heavy metals was compared with that of zero-valent iron (ZVI) of particle size 1.0 to 1.8 mm. The AMD used in the study was obtained from abandoned gold and coal mines. PERVC mixtures consisted of granite aggregate and ordinary Portland cement CEM I 52.5R (CEM I) or CEM I containing Class F 30% fly ash (30%FA) as a cement replacement material. ZVI was prepared from a mixture of silica sand and iron grit of specific sizes. PERVC and ZVI media were used to conduct batch reactor tests with AMD, for a period of 43 days at a ratio of 1 L of reactive material to 3 L of AMD. The quality of treated AMD was compared against effluent discharge standards. The contaminants Al, Fe and Zn were effectively removed by both PERVC and ZVI. Also, both adsorbents reduced Ni, Co and Cu to levels below those measured in raw AMD. However, PERVC was more effective in removing Mn and Mg while ZVI was ineffective. Although PERVC removed more heavy metals and with greater efficiency than ZVI, the PERVC-treated water showed high pH levels and exhibited elevated Cr6+ concentrations, owing to leaching from the cement and fly ash materials used in PERVC mixtures.

Assessment of the Suitability of Mine Water Treated with Pervious Concrete for Irrigation Use

In water scarce countries, the treatment and re-use of polluted mine water can reduce water shortage problem. In this study, the possible use of pervious concrete to treat Acid Mine Drainage (AMD) for irrigation of agricultural crops, was investigated. Pervious concrete mixtures consisting of 6.7 mm granite aggregate and plain portland cement CEM I 52.5R with or without 30% fly ash were prepared and used to conduct column studies on AMD. The AMD types used in the study were obtained from abandoned coal (TDB) and gold (WZ) mines. Physico-chemical parameters of water including the pH, electrical conductivity (EC), Total Dissolved Solids (TDS), along with element concentrations were analysed. Also the Sodium Adsorption Ratio (SAR), Soluble Sodium Percentage (SSP), and Kelly’s ratio (KR) of the treated AMD were calculated and compared against the water quality criteria for irrigation use. Results showed that treated TDB water was unsuitable for irrigation use owing to its high TDS, EC, SSP and KP values, even though its metal concentrations were reduced to satisfactory levels. Conversely, treated WZ water gave low SAR, SSP and KP indices, as well as satisfactory metal concentrations, indicating its suitability for use as irrigation water. The study shows that pervious concrete can be effective in treating AMD for irrigation use, but further research is needed to control high alkalinity and salinity levels in the treated water.

Analysis of Influence of the Dolomite Inactive Mineral Filler Quantity on Properties of Deep Cold Recycled Mixtures with Foamed Bitumen

The subject of research presented in article was an assessment of the impact of inactive mineral filler content, i.e. dolomite dust, on the recycled cold mix properties with foamed bitumen. The analysis of the impact of dolomite mineral dust was made on the basis of the experiment design type 33. It consisted of three levels of foamed bitumen factor in the range from 1.2% to 3.6% with a 1.2% step and the amount of mineral dust factor in range from 5% to 20% with a 7.5% step. Dolomite dust is a waste material derived from aggregate mining. Foamed bitumen was obtained from foaming process of the neat bitumen 50/70 at water temperature of 25ºC and its amount of 2.7%. In order to increase the cohesion of the recycled cold mix with foamed bitumen, Portland cement CEM I 32.5 R in amount of 2.0% was used. The assessment of the impact of quantitative variables was carried out in accordance with the adopted plan of the experiment that assumed the determination of physical and mechanical properties such as: resistance to climatic factors, dynamic modulus (E*) and phase angle. Analysis of the test results shown that factors quantity affects the variability of analysed features. In the entire scope of experiment plan, the obtained free space values met the requirements in required guidelines. The highest sealing of the recycled mixture was observed for the entire dolomite dust dosage but at maximum amount of foamed bitumen amounted to 3.6%. It was also observed that the maximum water resistance (TSR) was obtained for mixtures with a minimum amount of mineral dust (5%) as well as the maximum amount of dust in the recycled cold mix (20%). However, it was depended of the amount of foamed asphalt in a recycled mixture composition. The study also was considered the influence of the amount of dolomite mineral dust on the change in stiffness modulus tested by means of IT-CY and DTC-CY procedure. It was shown that either stiffness modulus measured by IT-CY or DTC-CY are foam bitumen and dust amount dependent. To assess the rheological properties, the direct compression-compression test (DTC-CY) was used. All samples were subjected to a cyclic sinusoidal constant strain with an amplitude of εo <25με. The tests were carried out in the temperature range (-7ºC, 5ºC, 13ºC, 25ºC, 40ºC) and loading time (0.1 Hz, 0.3 Hz, 1 Hz, 3 Hz, 10 Hz, 20 Hz). It was found a significant variability of recycled base stiffness depending on loading time and temperature.

Insights into the hydration of Portland cement under hydrothermal curing

The combined effect of temperature and vapor pressure on hydration reactions of three different types of Portland cements was studied using a laboratory autoclave. Oil well Portland cement Class G high sulfate resistant (HSR), Dyckerhoff Portland cement and Portland cement CEM I 42.5 R Extra were cured under hydrothermal conditions (165 °C–0.5 MPa and 220 °C–2.0 MPa) up to 7 days. In parallel, hydration reactions at laboratory conditions (25 °C–0.1 MPa) of these samples were also studied. Simultaneous thermogravimetric and differential thermal analysis measurements (TG/DTA) were mostly used to characterize the course of hydration under different curing conditions. X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry were used to identify the hydration products and to characterize the coupled effect of temperature and vapor pressure on microstructure and pore structure development. Also, mechanical properties were correlated with pore structure and scanning electron microscopy analysis. Different hydrothermal curing regimes resulted in sequential and overlapped hydration reactions with products including portlandite, ettringite, poorly crystalline C–S–H, hydrogarnet (C–A–S–H), α-C2SH, jaffeite (C6S2H3), scawtite (C7S6$${\bar{\text{C}}}$$H2) and reinhardbraunsite (C5S2H). Calcium silicate hydrate underwent systematic changes starting with the transformation of C–S–H gel formed during the non-equilibrium phases or under low-pressure hydrothermal conditions to α-C2SH, jaffeite and reinhardbraunsite with increasing hydrothermal temperatures. The gradual transition of amorphous C–S–H phases to α-C2SH, C6S2H3, C7S6$${\bar{\text{C}}}$$H2 and C5S2H has caused the deterioration of pore structure with corollaries of the increase in permeability and the decrease in mechanical properties. Moreover, different temperature peaks from 600 to 1000 °C denoting thermal decomposition of different calcium carbonate species were depicted at DTG curves. These are ranged from low to well-crystallized CaCO3.

Infrared spectr of SP–2VU superplastifying agent and a cement mortar with additive

To improve the concrete properties, various technological methods are used, the most accessible ones being the introduction of chemical additives into the concrete mixture, which can significantly reduce the costs level per unit of production; these additives improve concrete quality and effectiveness and reinforced concrete structures as well as increase their service life and buildings and structures in whole. This paper presents the results of studying the effect of introducing a superplasticizer with stabilizing effect of Polyplast SP – 2VU LLC Polyplast Novomoskovsk into concrete by analyzing the IR spectra of the additive in pure form and as part of hardened cement mortar (0.1–0.9%). Portland cement CEM I 42.5 B of Mordovcement OJSC was used as a binder; the aggregates were enriched with quartz sand from the Khromtsovsky deposit with a size of 2.4 and granite crushed stone of the Orsk deposit of 5–20 mm with water absorption of 0.2% . In the course of the work, the chemical composition of the additive SP2-VU itself and the hardened modified concrete composition were analyzed. Thus, the introduction of a modifier into a concrete composition leads to the change in its structure and strength characteristics. It was established with the help of IR spectra, that when the content of the additive in the cement mortar is 0.5%, a more ordered and stable hardened structure is formed. The reliability of the data obtained is confirmed by the identification of the main peaks. Due to the modification of concrete (at 0.3-0.5% in the concrete mix regulator concentration), the increase in the strength of the samples is more than 40%.

The influence of universal additive BEST on the concrete properties

In order to improve the properties of concrete, various chemical additives are introduced into the concrete mix which can significantly reduce the level of costs per unit of production, improve the quality and effectiveness of concrete and reinforced concrete structures, increase their service life as well as buildings and structures as a whole. This paper presents the results of the regulation of the setting speed, strength and frost resistance of concrete modified with the universal additive BEST LLC “Makra”. Portland cement CEM I 42.5 B of Mordovcement OJSC was used as a binder; the aggregates were enriched quartz sand from the Khromtsovskoye deposit with a size of 2.4 and granite rubble of the Orsk deposit of 5–20 mm with water absorption of 0.2% .The effect of the universal BEST additive on the construction and technical properties of concrete was studied by determining the binder system setting speed and the hardened composition strength characteristics. Data analysis showed that the introduction of a regulator in the amount of 0.3% into the concrete mixture contributes to the long-term preservation of its mobility (up to 4 hours) due to the water-proof modifier adsorption layer formation on the cement grains surface. With an increase in the content (0.5–1.0%) of BEST in the system the concrete setting speed acceleration was established due to the additive deflorulating effect. We have identified an increase in the strength characteristics of the modified (by 41%) concrete compared with no additional. Besides, the introduction of the universal additive BEST allows you to adjust the concrete frost resistance ~2 times possibly due to accelerated formation of calcium hydroxides gels.

Evolution of Salt Efflorescence on Clinker Face Walls

The lowering of building element aesthetics caused by salt efflorescences can have various characters. It depends mostly on types of wall component types, external environment conditions, and on-going physical and chemical processes. The active salts responsible for efflorescence appearance do not only worsen the wall look. They can also lead to lower durability because of microstructure destruction both in ceramic as well as in mortar. The type of mortar used for face clinker walls in essential way influences the limitation of efflorescences and discolorations which appear. Additionally, the way how wall is formed on the subsoil is a factor determining the character of salts appearing. In this work there is an analysis of the evolution of efflorescences appearing on two exemplary face walls made with various mortars. The walls were built with solid clinker bricks of traditional size 250x120x65mm in connection with two mortars: cement mortar based on portland cement CEM I 42.5, and cement-lime one. Additionally, during the research three different contacts of the wall with subsoil were tested: gravel layer, humus with lawn, and tight concrete band. The analysis lasted for ten years of wall exploitation in external environment. In the tested walls there were made chemical analyses for the quality and quantity of the appearing salts. There is also a raster picture of appearing efflorescence evolution made with AutoCad program during the research time period.

Static Analysis of Prestressed Floor Slabs HC500 with Changes in Tendon Adhesion to Concrete Induced by Penetration of Chloride Ions

Prestressed hollow-core slabs are suitable for various span applications in different types of buildings. Such structures are quick to mount and do not require boarding system or assembly supports reducing deflection, which is an economic asset. The performed analysis included HC-500 slabs made of C50/60 concrete with w/c ratio of 0.31, with Portland cement CEM II 52.5 R. Strength of such structures is determined by, among other things, chloride ion concentration at the interface between the surface of prestressing tendons and concrete. Corrosion products, induced by chloride ions, will certainly reduce stress of adhesion to concrete, and consequently, second-order momentum in the structure. It may be difficult to draw firm conclusions about the predicted strength of analysed slabs on the basis of the obtained results. Therefore, we performed the static analysis including the changes in tendon adhesion to concrete caused by corrosion. We also analysed the bearing capacity of slabs according to concrete cover thickness of upper and lower tendons. The analyses included results from the accelerated tests on chloride ion penetration to cylindrical elements drilled directly from the top surface of prefabricated prestressed floor slabs HC500-19/R120. Those results were used to determine the diffusion coefficient of chloride ions into concrete, from which the analysed slabs were made. The value of diffusion coefficient for the tested concrete was used to illustrate results for changes in the bearing capacity over time. We determined times, after which those tendons could corrode, assuming that penetration of chloride ions is observed only at the surface of the upper floor slab. The obtained results were used to develop recommendations and draw conclusions for further tests.

Physico-Mechanical Features of Portland Cement Mortars Replaced Partially with Aluminium Cement

The purpose of the research was to recognize the effect of the addition of aluminium cement on the properties of cement mortar made of Portland cement CEM I 42.5R. Alumina cement is a hydraulic binder. It is a finely ground organic material that when mixed with water binds as a result of reactions and hydration processes. After hydration, stable hydrate phases form and, as a consequence, the material strength parameter is obtained. The main constituent is calcium aluminate (CaO⋅Al2O3), in smaller amounts there are: calcium aluminate, dicalcium silicate and calcium aluminium silicate or gelenite. Hydraulic hardening of aluminium cement occurs mainly through calcium hydration but other chemicals may also take part in the hardening process. The specific chemical composition of aluminium cement and the fact that calcium hydroxide is not released during hydration allows the leaven to resist many aggressive factors. Therefore, in the literature, we can meet guidelines so that the w / c ratio is not greater than 0.40 for applications to structural elements. The article discusses the results of laboratory tests on the impact of replacing Portland cement with aluminium cement in the amount of 10%, 20%, 50%, 100% on the physical and mechanical properties of mortars. The rheological properties of mortars, i.e. consistency, setting time and parameters of hardened mortars were examined, among others compressive and bending strength, capillary rise and absorbability. Compressive strength and bending strength were tested after 1, 7 and 28 days on samples with dimensions 4 × 4 × 16 cm. Absorption and capillary rupture were tested 28 days after being formed on standard bar beams 4×4×16cm. The mortar was made with a constant coefficient w/c = 0.38.

The effect of fly ash additive on the resistance of concrete to alkali silica reaction

Concrete is the most widely used construction material obtained after the setting of the mix composed course and fine aggregates, cement and water. The main properties of concrete are determined by the quality and characteristics of aggregates, w/c ratio, and the uniformity of mix compaction. Materials used: Portland cement CEM I 42.5 R, 0/4 fraction sand, 4/16 fraction gravel, fly ash, superplasticizer, and water. 7 batches of specimens were made with different fly ash content: 0%, 15%, 25%, 35%, 45%, 55%, 65% (replacing cement in the mix, %). Compressive strength and flexural strength, water absorption, density, ultrasonic pulse velocity, and alkali silica reaction resistance were tested in modified concretes against the expansion of the specimens. Concrete, where 65% of cement is replaced by fly ash, has higher density, ultrasonic pulse velocity, and lower water absorption rate. Subsequently, the expansion of modified specimens is lower. All these characteristics improve the alkali silica reaction resistance of concrete. The obtained relationship between the fly ash content in concrete mix, the change of ultrasonic pulse velocity and expansion of the specimen is used to evaluate the alkali silica reaction effect on concrete. The tests revealed that concrete modified with 65% of fly ash has better durability and alkali silica reaction resistance characteristics and can be used in construction works.

Flow properties of finely dispersed binder

This article contains information about strengthening the under-ground parts of buildings and restoration of their bearing capacity, along with solutions of urea-formaldehyde resin and solutions based on sodium silicate (which have a number of significant drawbacks, such as short-lived strengthening, low strength of reinforced soil (0.1-0.5 MPa), brittle destruction under dynamic loads, environmental pollution), using impregnation compositions based on fine mineral binders. This compositions, with the name «Mikrodur», are obtained on the basis of air separation of Portland cement CEM I 52.5 (PC D0 M600) and fine-divided blast furnace slag. The method of preparation of suspension on the basis of finely dispersed binder is considered. The main characteristics determining the finely dispersed binder suspension, such as viscosity and stability of the injectable suspension (sedimentation), are established. It is proved that the indexes of viscosity and stability of solutions depend on the method of their preparation, water/binding ratio and chemical admixtures. A variety of finely dispersed binders grades on mineral composition allows providing ground, stone and concrete structures of underground constructions stabilization taking into account various requirements: strength enhancement and anti-filtration properties of the strengthened masses, their resistance to various aggressive influences, the possibility of hardening in conditions of negative temperature, acceleration of a strength enhancement.

Frost resistance of cement composites prepared on the basis of waste water from a concrete plant

Abstract This article presents the results of a research dealing with the use of waste water from concrete industry as a possible substitution of mixing water during the production of cement composites. This experimental research involved the preparation of two recipes of cement composites, named R1 and R3. Mixing water in these recipes was replaced with waste water from a concrete plant in the amount of 25, 50, 75 and 100%. Samples of recycled waste water, which were tested for the content of sulphates, chlorides and alkali according to ČSN EN 1008, were taken in order to determine the properties of waste water from a concrete plant. The prepared test specimens were tested for frost resistance after 100 freezing cycles according to ČSN 73 1322. The results of the frost resistance test showed that the required value of the frost resistance coefficient of 0.75 according to ČSN 73 1322 was achieved only in case of recipe R1 based on Portland cement CEM I 52.5R and 75 and 100% substitution of the mixing water with recycled water from a concrete plant.

Analysis of the Properties of Expansive Concrete With Portland and Blast Furnace Cement

AbstractThe properties of expansive concretes made of two types of cement: Portland cement CEM I and blast furnace slag cement CEM III were tested. The expansion of the concrete was caused by using an expansive admixture containing aluminium powder added in an amount of 0.5; 1 and 1.5% of cement mass. It was found that the compressive strength of concrete with CEM I decreased after using an expansive admixture in the amount of more than 0.5% of the cement mass. The compressive strength of concrete with CEM III decrease after addition of admixture in the entire range of dosages used. On the basis of electrochemical measurements, it was found no influence of an expansive admixture on corrosion of reinforcing steel. The use of an expansive admixture causes a slight increase in the effective diffusion coefficient of chloride ions in concrete.

THE INFLUENCE OF PLASTICISING ADMIXTURES ON DRYING SHRINKAGE OF CEMENTITIOUS COMPOSITES

This article presents a research into the impact of plasticising admixtures on drying shrinkage of cementitious composites by evaluating the effectiveness of plasticising. Materials used in the study: Portland cement CEM I 42.5 R, plasticiser LS (modified lignosulphonates based), superplasticiser PCE (synthetic polycarboxylate esters based), superplasticiser MAP (modified acrylic polymers based), sand and water. The percentage change of plastic viscosity of cement paste indicates the effectiveness of plasticising of cementitious composites. The change of plastic viscosity has been tested by adding a specific amount of plasticising admixtures. The effectiveness of plasticising of pastes were tested using rotational viscometer. Chemical admixtures content in pastes varied from 0 to 1.2%. Drying shrinkage was tested based on length change of the specimens with fine aggregates. The method to minimise drying shrinkage of composites was established through use of plasticising admixtures. It has been found that by increasing plasticising admixture dosage from 0 to 1.2% the following changes occur: LS plasticising effectiveness increases by 35% while drying shrinkage decreases by 8%; MAP plasticising effectiveness increases by 70% while drying shrinkage decreases by 16%; PCE plasticising effectiveness increases by 80% while drying shrinkage decreases by 20%.

Numerical identification of the thermal properties of early age concrete using inverse heat transfer problem

The procedure of numerical identification of thermophysical properties of concrete during its hardening is presented. Heat of cement hydration, thermal conductivity and specific heat are determined for purpose of modelling temperature evolution in massive concrete elements. The developed method is based on point temperature measurements in a cylindrical mould and the numerical solution of the inverse heat transfer problem by means of direct search optimization algorithm. The determined thermal characteristics of concrete are not constant and depend on the maturity of concrete. The procedure was verified on set of concrete mixes designed with Portland cement CEM I 42.5R and Portland-slag cement CEM II/B-S 32.5 N. Calcareous fly ash was also used for partial replacement of cement in the mixtures. The obtained results have been compared with experimentally measured temperature in concrete and a fair agreement has been found.