Diana Bajare

Influence of superabsorbent polymers on hydration of cement pastes with low water-to-binder ratio

Internal curing with superabsorbent polymers (SAP) is a method for promoting hydration of cement and limiting self-desiccation, shrinkage and cracking in high-performance, and ultra high-performance concrete with low water-to-binder ratio. SAP are introduced in the dry state during mixing and form water-filled inclusions by absorbing pore solution. The absorbed solution is later released to the cement paste during hydration of the cement. In this paper, cement pastes with low water-to-binder ratios incorporating superplasticizer and different dosages of SAP and corresponding additional water were prepared. Reference cement pastes without SAP but with the same amount of water and superplasticizer were also mixed. Isothermal calorimetry was used to measure hydration heat flow. Water entrainment by means of SAP increased the degree of hydration at later hydration times in a manner similar to increasing the water-to-binder ratio. Addition of SAP also delayed the main calorimetric hydration peak compared to the reference pastes, however, in a less prominent manner than the increase in water-to-cement ratio.

Performance Analysis of Air-to-Water Heat Pump in Latvian Climate Conditions

Abstract Strategy of the European Union in efficient energy usage demands to have a higher proportion of renewable energy in the energy market. Since heat pumps are considered to be one of the most efficient heating and cooling systems, they will play an important role in the energy consumption reduction in buildings aimed to meet the target of nearly zero energy buildings set out in the EU Directive 2010/31/EU. Unfortunately, the declared heat pump Coefficient of Performance (COP) corresponds to a certain outdoor temperature (+7 °C), therefore different climate conditions, building characteristics and settings result in different COP values during the year. The aim of this research is to investigate the Seasonal Performance factor (SPF) values of air-to-water heat pump which better characterize the effectiveness of heat pump in a longer selected period of time, especially during the winter season, in different types of residential buildings in Latvian climate conditions. Latvia has four pronounced seasons of near-equal length. Winter starts in mid-December and lasts until mid-March. Latvia is characterized by cold, maritime climate (duration of the average heating period being 203 days, the average outdoor air temperature during the heating period being 0.0 °C, the coldest five-day average temperature being −20.7 °C, the average annual air temperature being +6.2 °C, the daily average relative humidity being 79 %). The first part of this research consists of operational air-towater heat pump energy performance monitoring in different residential buildings during the winter season. The second part of the research takes place under natural conditions in an experimental construction stand which is located in an urban environment in Riga, Latvia. The inner area of this test stand, where air-to-water heat pump performance is analyzed, is 9 m2. The ceiling height is 3 m, all external wall constructions (U = 0.16 W/(m2K)) have ventilated facades. To calculate SPF, the experimental stand is equipped with sensors which provide measurements for electricity consumption and gained heat energy.

Restoration of the historical brick masonry

Publisher Summary The architectural heritage of Latvia mainly consists of manufactured materials. The Building of Riga City Council, Fortification Wall of Riga, Turaidas Palace, and Ventspils Castle are few examples of historical buildings of Latvia from 12th –17th centuries. These buildings were made from brickwork. Migration of the water-soluble salts and influence of frost in the winter are the major causes of mechanical damages in these structural brickworks because of crystallization and growing of salts or ice crystals. An increased corrosion of single brick or brick masonry fragments in the architectural monuments of the Middle Age was observed; and hence, it is necessary to replace these bricks with the new ones of the same size, color, and physical properties. The modern bricks produced in Latvia do not have the same physical and chemical characterizations; and therefore, new materials suitable for the restoration work of brick masonry need to be developed. The chapter describes the analyses of the historical bricks to determine their manufacturing processes, and then development of similar materials from local clays for the replacement of damaged original bricks in the historical buildings. The analyses are conducted by visual inspection, chemical analyses, X-ray diffraction, and mercury porazimeter for pore size distribution. The chapter discusses the results obtained from the analyses of the historical bricks.

Alkaline Activated Material for pH Control in Biotechnologies

By using industrial aluminium recycling waste, recycled silicate glass from outworn fluorescence lamp recycling plant, calcined kaolinite clay supplemented with alkali activator with different silicate modulus the new type of porous material for biotechnologic processes without the need for additional equipment for pH control was researched. This controlled-release system contains an alkali activated matrix in which NaOH crystals are encased. In this study ability to release NaOH per time in water according to material composition and structure were investigated. Three alkaline activated materials AAM 7.5, 10 and 12.5, with different alkali activator content were characterized.

The Formation of Microstructure in High Strength Concrete Containing Micro and Nanosilica

This article presents the results of microstructural investigation of high strength concrete containing microsilica and nanosilica (amorphous SiO2) as an active pozzolanic admixture. Micro and nanosilica react with calcium hydroxide producing calcium silicate hydrates (C-S-H), thus the voids and pores within concrete are filled and new minerals are formed in the gaps between cement grains and aggregate particles. Unreacted round microsilica and nanosilica particles were registered using SEM even in 6 month old samples. The compressive strength results indicate that concrete still continues to harden after the 28-days of curing.

The Effect of Activator on the Properties of Low-Calcium Alkali-Activated Mortars

Properties of the low-calcium alkali-activated materials (AAMs) made from the metakaolin, waste glass and sand were tested in this research. Specimens with dimensions 40x40x160mm were prepared. The correlation between development of microstructure and concentration of NaOH solution used for preparing of the AAMs was observed. Structure investigation with SEM and FTIR was performed to describe the formation of microstructure in low-calcium AAMs. The research results aimed that the improvement of physical and mechanical properties of the AAMs with increasing the activator’s concentration from 2 to 10 mol/kg H2O were in concordance with the structure development of AAM. The 28 days old AAMs with a compressive strength up to 31MPa and water absorption lower than 2% were obtained by using activator with concentration 10 mol/kg H2O.

Effect of Ground Glass Fineness on Physical and Mechanical Properties of Concrete

This research is focused on the development of concrete mix by using borosilicate glass micro-filler obtained from the waste of outworn fluorescent lamps. The task of the research is to find the optimal fineness of glass particles, which can improve packing of microparticles in cement matrix to increase the strength properties of concrete. Previous research as well as chemical composition of glass proved that ground glass can be used as an effective concrete component. Borosilicate glass micro-fillers with different grinding degree were used in experiments. Particle grading was determined by using the laser diffraction method. The morphology of microparticles was investigated. The effect of glass powder on cement setting time was checked. It was determined that fine glass particles powder produces a long-term hardening effect. Experimental work includes preparation of samples from standard concrete and concrete with borosilicate glass micro-filler (with particles of different sizes and mixed in different proportions) and testing after the ageing period of 7 and 28 days. The long-term hardened samples were also tested. The compressive strength of concrete samples is decreasing when rough glass powder is used as cement replacement. At the same time fine glass filler with particle size up to 0.1–10 μm allows improvement in mechanical properties of concrete and makes it possible to replace up to 25% of the cement without impairing the strength characteristics of concrete. As a result, concrete with improved water resistance and durability was obtained.

Influence of fillers on the alkali activated chamotte

Alkali-activated materials (AAM) exhibit remarkable high-temperature resistance which makes them perspective materials for high-temperature applications, for instance as fire protecting and insulating materials in industrial furnaces. Series of experiments were carried out to develop optimum mix proportions of AAM based on chamotte with quartz sand (Q), olivine sand (OL) and firebrick sawing residues (K26) as fillers. Aluminium scrap recycling waste was considered as a pore forming agent and 6M NaOH alkali activation solution has been used. Lightweight porous AAM have been obtained with density in range from 600 to 880 kg/m3 and compressive strength from 0.8 to 2.7 MPa. The XRD and high temperature optical microscopy was used to characterize the performance of AAM. The mechanical, physical and structural properties of the AAM were determined after the exposure to elevated temperatures at 800 and 1000°C. The results indicate that most promising results for AAM were with K26 filler where strength increase was observed while Q and OL filler reduced mechanical properties due to structure deterioration caused by expansive nature of selected filler.

Structural Investigation of Alkali Activated Clay Minerals for Application in Water Treatment Systems

Alkali activation technology can be applied for a wide range of alumo-silicates to produce innovative materials with various areas of application. Most researches focuse on the application of alumo-silicate materials in building industry as cement binder replacement to produce mortar and concrete [1]. However, alkali activation technology offers high potential also in biotechnologies [2]. In the processes where certain pH level, especially alkaline environment, must be ensured, alkali activated materials can be applied. One of such fields is water treatment systems where high level pH (up to pH 10.5) ensures efficient removal of water pollutants such as manganese [3]. Previous investigations had shown that alkali activation technology can be applied to calcined clay powder and aluminium scrap recycling waste as a foam forming agent to create porous alkali activated materials. This investigation focuses on the structural investigation of calcined kaolin and illite clay alkali activation processes. Chemical and mineralogical composition of both clays were determined and structural investigation of alkali activated materials was made by using XRD, DTA, FTIR analysis; the microstructure of hardened specimens was observed by SEM. Physical properties of the obtained material were determined. Investigation indicates the essential role of chemical composition of the clay used in the alkali activation process, and potential use of the obtained material in water treatment systems.

Microstructural Investigations of Ultra-High Performance Concrete Obtained by Pressure Application within the First 24 Hours of Hardening

Abstract In this study, the effect of pressure application (0-50 MPa) to fresh concrete right after casting and during the first 24 hours of hardening has been examined. Supplementary cementitious materials in a form of silica fume, nanosilica and ground quartz sand were used. The aim of pressure application was to reduce porosity, thus improving concrete mechanical properties. Considerable reduction in porosity and a subsequent increase in compressive strength reaching the level of Ultra-High Performance Concrete (UHPC) were achieved. Mechanical and physical properties were tested and gas sorption porosimetry, mercury intrusion porosimetry (MIP), X-ray diffraction (XRD), as well as scanning electron microscopy (SEM) were used for material characterization.