Ivan Janotka

THE HYDRATION PHASE AND PORE STRUCTURE FORMATION IN THE BLENDS OF SULFOALUMINATE-BELITE CEMENT WITH PORTLAND CEMENT

Abstract Sulfoaluminate-belite (SAB) cements are an attractive class of low-energy cements from the viewpoint of saving energy and releasing less CO 2 into the atmosphere during their production. Their hydraulic activity, however, does not match that of the ordinary Portland cement (PC) and needs improvement before they can be used on their own. However, SAB cements when blended with PC have the potential to be used effectively in traditional applications as shown by this study. Mortars made with blends of SAB cements and PC, and a cement-to-sand ratio of 1:3 by weight and a water-to-cement ratio of 0.5, indicate a superior protection against corrosion of steel to those made with blends of PC and blast-furnace slag (BFSPC). The prepared mortars were stored at 20 °C for 90 days under either a 60% relative humidity (RH)–dry air, or 100% RH–wet air conditions. With further improvement in the SAB cement quality through better understanding of their characteristics, a genuine competition between SAB/PC and BFSPC can be expected in practice.

Geosynthetic mat Tatrabent—development, production and application

Abstract The geotechnical and chemical approach to the evaluation of blended mineral fillers in a geosynthetic mat for sealing purposes is introduced. Properties measured include water sorption characteristics, heavy metal sorption, neutralization ability, occlusion of saturated vapors of water and nitrogen dioxide and permeability. Bentonite is the main component in the blend; zeolite and diatomite are added minerals. All materials are mined in Slovakia. Bentonite–zeolite mineral filler is used in the geosynthetic mat TATRABENT manufactured since 1996. The significance of the relation between liquid limit ( w L ) and swell characteristics like water adsorption by Enslin ( E S ) free swell and one-dimensional swelling has been studied to assess the quality of mineral fillers. Similarly, the relation between liquid limit and coefficient of permeability of mineral fillers is concerned herein. The review of recommended properties for blended mineral filler of Tatrabent is given as well (300%≤ w L E S k ≤5×10 −11 m s −1 and heavy metal sorption ability >95%/24 h). These values are optimal for regularly tested and certified Tatrabent mineral filler with the weight ratio of bentonite to zeolite 9:1 in the final product. The difference between Tatrabent mineral filler and those recently used in waste landfills in the world is that Tatrabent mineral filler is the blend of bentonite and zeolite or diatomite while the others consist only of natural or activated bentonites. The purpose of this contribution is to suggest directions for the optimal use of blended mineral fillers used in the geosynthetic mat Tatrabent acceptable in landfill construction for waste containment on the basis of obtained results.

Experimental Evaluation of Properties of 120 Years Old Concretes at Two Concrete Bridges in Slovakia

Currently there are two bridges older than 120 years under reconstruction in Slovakia. One of them is the Old Bridge in Bratislava, which has been built in 1891 and has a steel superstructure supported by concrete piers. The other one is the Monier Arch Bridge in Krásno nad Kysucou, which has been built in 1892. Since only limited information about the properties of such an old concrete is available, it was almost impossible for the designer to verify the load bearing capacity of these bridges and to design their reconstruction efficiently. To verify the properties of these concretes drill cores were made on both bridges, some of them being more than 20 meters long [17]. After that the measured concrete properties were used to confirm or modify the reconstruction method proposed in the preliminary design. Our paper deals with some mechanical properties measured on these more than 120 years old concretes.

NTCC 2017: Long-Term Observation of the Resistance of Novel Hybrid Cement Exposed to Sulphate Solution

This work is aimed to investigate four-years impact of 5 % sodium sulphate solution on the mortar made of novel hybrid cement H-CEMENT, being prepared with maximal content of wastes and by-products and only 20 % wt. of Portland cement clinker, compared to that prepared with the reference CEM I 42.5 N (PC). H-CEMENT for its specific material composition does not meet the criteria for inclusion in the cement kinds reported in EN 197-1 but complies with all of the hygienic regulations and standards imposed on similar building materials.

Physical and Chemical State of the Concrete Piers of the Former Franz Joseph Bridge Built in 1891

This article discusses the properties of concrete within the piers of the Old Bridge in Bratislava (former Franz Joseph Bridge). It was the first permanent bridge across the river Danube in Bratislava as well as within the present territory of Slovakia. Mechanical, physical and chemical properties were verified on core drills, some of them being almost 23 m long. The concretes were tested for dynamic and Young’s elasticity module and compressive strengths. Subsequently the fines of concrete specimens were studied by the X-ray diffraction, TG-DTA and mercury intrusion porosimetry techniques and also by chemical analyses and SEM observations. The piers were made from 5 different concrete kinds. The concrete in the caissons and in the piers does not fulfil the criteria for structural concrete defined in the present European standards. This finding seriously suggests that carrying capacity of the piers after the reconstruction of the bridge, without any strengthening would become questionable.

Basic Characteristics of Green Cements of CEM V/A and V/B Kind

The reduction of the clinker to addition ratio is becoming of main technological importance because energy saving potential by process optimization at the cements manufacture is almost exhausted. The main properties of composite cements of CEM V/A and CEM V/B kinds of Austrian (AT) and Slovak (SK) provenance with cement clinker contents between 45.1 % (CEM V/A-AT) – 52.9 % (CEM V/A-SK) and 26.9 % (CEM V/B-AT) – 30.9 % (CEM V/B-SK), and reference Slovak CEM I 32.5 R cement containing 95 % of the clinker were tested. The composite cements consist of cement clinker with following additions: blast furnace slag, fly ash and natural pozzolan - zeolite. Basic cement properties (normal consistency, initial and final set, volume stability) and fresh mortar properties (workability, volume density, air content) and strength parameters using standard mortars with W/C of 0.5 are introduced. Laboratory-made CEM V/A concrete specimens (AT and SK) demonstrated 90-day cube compressive strength between 49.8 – 50.9 MPa in water and 45.2 – 48.2 MPa in 60 % R.H. dry air; and those of CEM V/B concretes between 39.7 – 40.9 MPa in water and 26.9 – 38.7 MPa in 60 % R.H. dry air opposite to 53.6 MPa in water and 48.3 MPa of the CEM I 32.5 R concrete kept 90 days in 60 % R.H. dry air at (20 ± 1) °C. The use of CEM V/ (A, B) cements for structural concrete is strongly restricted by normative limitations in European countries. In order to improve this circumstance in Austria and Slovakia, the common research project was solved between 2010 and 2012 with the aim to show application possibilities of CEM V/A and CEM V/B cements for common usage in the structural concrete and ready-mixed concrete.

Effect of Metakaolin Sand on Properties of Cement Composites

The Slovak natural raw material kaolin sand containing 36 wt.% of kaolinite from Vyšný Petrovec deposit was thermally transformed at 650 °C for 1 hour to the metakaolin sand with relevant content of metakaolinite. Behaviour of cement composites having replacement of Portland cement with metakaolin sand including 0; 5; 10 and 15 wt.% of metakaolinite and water to solids ratio of 0.5 cured in water for 28 days and 90 days was studied by thermal analysis, X-ray diffraction analysis and mercury intrusion porosimetry analysis. The study concerned calciumsilica hydrate and calcium aluminate hydrate formation, portlandite dehydroxylation and calcite decarbonation. The influence of curing time and metakaolinite content were estimated. The replacement of Portland cement by metakaolin sand led to positive effect on relevant compressive strengths. The changes in microstructure involved especially reduction in portlandite content and pore structure refinement.