Effect of Microstructure on Frost Durability of Rock in the Context of Diagnostic Needs

AbstractProblematic rock classification criteria used in civil engineering require correction. Particular attention should be paid to frost resistance test methods and criteria of acceptable absorption levels. The classification of frost resistance levels may be incorrect due to insufficient number of freeze-thaw cycles, and the criterion of rock absorption is inaccurate. Based on the results of research completed to date, the authors conclude that all rocks with capillary volumetric absorption below 0.6% are highly frost resistant, regardless of their origin. All rocks with capillary volumetric absorption above 1.5% are not frost resistant to a greater or lesser degree. Rocks with capillary volumetric absorption between 0.6% and 1.5% may show both low and high frost resistance. This group of rocks is characterized in this article. The structural features compared include mineralogical composition (derivatography and X-ray analysis), appearance and size of crystallite (analysis with an optical microscope, and SEM). The texture features evaluated include total porosity, pore size distribution MIP, capillary water absorption, vacuum absorption, and the degree of filling the pores with water. It has been found that increasing the number of freeze-thaw cycles allows better assessment of the rock's potential durability. The capillary water absorption in combination with the degree of filling the pores can be an effective durability indicator for use in the classification of rock construction products

Testing alkali‐reactivity of selected concrete aggregates

In the present paper, results of alkali reactivity tests for selected silica aggregates, both rapid and slow alkali reactive, with the use of ASTM procedures, have been presented. The tests have covered the determination of the aggregate silica content dissolved in a solution of sodium hydroxide; scale of the expansion of mortar and concrete bars with the silica aggregate and high‐alkali cement; as well as scale of the expansion of the mortar bars stored in a sodium hydroxide solution at 80 °C. Exemplary photographs of the microstructure of alkali reaction products for the selected silica aggregates have also been presented. Summing up the results of standard methods of the aggregate testing, considering their alkali sensitivity, the method which tests the deformation of the concrete bars including the aggregate at issue and increased alkali content cement seems to be the most conclusive. However, the test duration up to 180 days is too short, particularly for defining the slow‐reactive aggregates reactivity, such as, for example, granites or quartzites. A major diagnostic symptom which confirms the occurrence of the alkali‐aggregate reaction is the presence of the reaction products (alkali silicate gel) in the concrete. Atrinktųjų betono užpildų šarminio reaktyvumo tyrimai Santrauka Nagrinėjami specialiųjų silicio užpildų reaktyvumo eksperimentinių tyrimų rezultatai. Analizuojama, kaip nustatomas greitasis ir lėtasis šarmų reaktyvumas taikant ASTM metodiką. Silicio kiekis užpilde nustatytas natrio hidroksido tirpale. Plėtimosi tyrimams buvo pagamintos skiedinio ir betono sijos su silicio turinčiais užpildais ir aukšto šarmingumo cementu. Skiedinio sijos buvo laikomos 80 °C temperatūros natrio hidroksido tirpale. Pateiktos minėtųjų užpildų šarminių reakcijų produktų mikrostruktūros nuotraukos. Šarminio jautrumo atžvilgiu apibendrinant užpildų tyrimų standartiniais metodais rezultatus galima teigti, kad betono sijų deformacijoms didžiausią įtaką turi šarmų kiekis cemente. Tačiau 180 dienų bandymų trukmė per trumpa, kad būtų galima nustatyti lėtai vykstantį užpildų reaktyvumą, ypač tokių užpildų kaip granitas ar kvarcas. Pagrindinis diagnostikos požymis, parodantis, kad vyksta užpildų šarminė reakcija, yra reakcijos produktų (šarminio silikato gelio) pasirodymas betone. First Published Online: 14 Oct 2010 Reikšminiai žodžiai: šarminė silicio reakcija, bandymų metodas, SEM

Properties of a Three-Component Mineral Road Binder for Deep-Cold Recycling Technology

This study examined the physical properties of a three-component mineral binder that is typically used in deep-cold recycling. Test binders were produced using Portland cement, hydrated lime, and cement bypass dust (CBPD) as a byproduct derived from cement production. The suitability of CBPD for use in road binders was assessed. Effects of the three-component binder composition on the setting time, soundness, consistency, and tensile and compressive strengths of the cement pastes and mortars were determined. The pastes and mortars of the same consistency obtained at different w/b ratios were tested. On this basis, the mixture proportions resulting in road binders satisfying the requirements of PN-EN 13282-2:2015 were determined. By mixing cement, lime, and CBPD during the tests, binder classes N1 to N3 were obtained. The replacement of 40% of cement mass with the CBPD high in free lime produced road binders suitable for recycled base layers. The total content of CBPD and hydrated lime in the road binder should not exceed 50% by mass. The potential risk of mortar strength reduction due to KCl recrystallization was discussed

Microscopic methods for analysis of mortars from historical masonry structures

The process of historical building conservation includes the repair of mortars eroded due to material and environmental factors. Identification of old mortar constituents is necessary to enable duplicating the material. Information on the binder and aggregate types and contents can be obtained from microscopic observation used in combination with instrumental methods. This paper presents the results of microstructure and mineral composition tests of mortars collected from the walls of thirteenth century buildings. A combination of techniques was used, which included X-ray diffraction, transmitted light optical microscopy and scanning electron microscopy with micro-area elemental composition analysis. The test results revealed porous lime and sand mortars with a binder-aggregate ratio often beyond the commonly adopted values. The mortars contained sand grains of up to 0.5 mm and larger pieces of limestone, flint, feldspar and brick. Transmitted light optical microscopy and scanning microscopy were found to be essential techniques for mortar characterization in existing buildings and structures

Mikrostruktura i skład fazowy zapraw z XVII-wiecznych budowli sakralnych

This work aims to characterize the microstructure of mortars derived from the walls of sacred buildings from the 17th century. The tests were carried out using the X-ray diffraction method, differential thermal analysis and scanning microscopy combined with the analysis of the elemental composition in the micro area. The results of this study show that the materials bonding the elements of the wall in historic buildings are porous sand-lime mortars with an increased binder-to-aggregate ratio, also containing limestone crumbs, flints and feldspars, and fragments of bricks larger than sand particles. The binder is fully carbonated calcium hydroxide, with no pozzolanic additives. The results of the microstructure and phase composition tests of mortars used for bonding wall elements in buildings constructed at the end of the 16th and early 17th centuries can be used to select the composition of mortars used in the renovation and repair of historic buildings.Celem pracy jest charakterystyka mikrostruktury zapraw pobranych z muru sakralnych budowli XVII-wiecznych. Badania wykonano metodą dyfrakcji rentgenowskiej, termicznej analizy różnicowej oraz mikroskopii skaningowej połączonej z analizą składu pierwiastkowego w mikroobszarze. Wyniki przeprowadzonych badań wykazały, że zaprawy łączące elementy muru w budowlach historycznych są porowatymi zaprawami wapienno-piaskowymi, o zwiększonym stosunku spoiwa do kruszywa, zawierają także w swoim składzie okruchy skał wapiennych, krzemieni i skaleni oraz fragmenty cegieł o większych rozmiarach niż ziarna piasku. Spoiwo stanowi w pełni skarbonatyzowany wodorotlenek wapnia, niezawierający dodatków pucolanowych. Wyniki badań mikrostruktury i składu fazowego zapraw stosowanych do spajania elementów muru w budowlach wznoszonych w końcu XVI i na początku XVII wieku mogą posłużyć do doboru składu zapraw stosowanych przy renowacji i naprawach budowli historycznych

Chemical corrosion of external stairs – case study

On the basis of examinations of the efflorescences formed on the concrete surface, an attempt was made to analyze the sources of concrete corrosion without entering inside the construction. The concrete stairs revealed the symptoms of leaching, as a result of alkali-aggregate reactions developing beneath the surface. As a result of this corrosion process and the carbonation propagating from the concrete surface, the carbonate efflorescences were found. Their phase composition was determined by X-ray diffraction. In order to identify whether the efflorescences were the results of the alkali-silica reaction or alkalicarbonate reaction, the microstructure was investigated using the scanning electron microscope together with energy dispersive spectroscopy

The impact of lithium nitrate on the physical and mechanical properties of Portland cement)

The effectiveness of lithium nitrate as a chemical additive which reduces the negative effects of alkali aggregate reaction was subject to research by scientists in many centres around the world. The literature data on the impact of lithium nitrate on the physical and mechanical properties of cements are rare. Without a precise definition of the impact of lithium nitrate on the cement properties, it is extremely hard to determine its real advantages in practical usage. In this paper, studies were undertaken to assess the impact of LiNO3 on the properties of pastes and mortars with Portland cement. The rate of hydration of the cement with lithium additive was examined by isothermal calorimetry, measurements of setting time and phase composition of cement pastes in the initial stages of hydration. The influence of the admixture on the compressive strength development of mortars after 2, 7 and 28 days of hardening was also researched. Results indicate that lithium nitrate accelerates the early hydration of Portland cement, affecting the precipitation of hydration products. The compressive strength of mortars with lithium admixture decrease after 28 days, although 2 an 7-day strength were greater than the control mortars

Sposoby ograniczenia reaktywności kruszywa żwirowego

Effectiveness of selected chemical admixtures and mineral additives to mitigate alkali-silica reaction was compared based on reactive gravel aggregate. Lithium compounds in the form of nitrate and lithium polysilicate were used as chemical admixtures. Natural pozzolans containing zeolite were used as mineral additive. Efficiency of the additive was enhanced by modification with ammonium ions. Linear changes of mortars with crushed gravel aggregates were studied with the accelerated and long-term methods. Additionally, scanning electron microscopy was used for microstructural observations. It was demonstrated that at elevated temperatures the application of lithium compounds provided better protection. Under conditions similar to those in the field, 20-30% of natural pozzolans proved to be more effective in inhibiting the expansion. Regardless of the method of protection applied, the presence of alkali-silica reaction products was detected in the microstructure of the mortars.Na przykładzie reaktywnego kruszywa żwirowego porównano efektywność ograniczenia reakcji alkalia-kruszywo przy pomocy wybranych domieszek chemicznych i dodatków mineralnych. Jako domieszki chemiczne zastosowano związki litu w postaci azotanu i polikrzemianu litu. W przypadku dodatków mineralnych zastosowano naturalną pucolanę, zawierającą zeolit, której efektywność zwiększano poprzez modyfikację jonami amonowymi. Wykonano badania zmian liniowych zapraw z rozdrobnionym kruszywem żwirowym metodą przyspieszoną i długoterminową. Dodatkowo wykonano obserwacje mikrostruktury z wykorzystaniem elektronowego mikroskopu skaningowego. Wykazano, że w warunkach podwyższonej temperatury lepsze zabezpieczenie uzyskano po zastosowaniu związków litu. W warunkach zbliżonych do eksploatacyjnych zastosowanie 20-30% pucolany naturalnej skuteczniej hamowało ekspansję zapraw z kruszywem reaktywnym. Niezależnie od sposobu zabezpieczenia, w mikrostrukturze zapraw wykryto obecność produktów reakcji alkalia-krzemionka