We present design and properties of combined air lime-white cement structural injection grouts containing 17.5% of air lime, 7.5% of cement and 75% of limestone filler, using white Portland cement. Time evolution of the grout setting process during hydration from early to late stages was monitored by NMR spectroscopy and compared to pure cement-paste control samples. The grout setting is significantly slowed down (by more than 10 days). The compressive strengths of the grouts were found in the range 1.5 - 2.5 MPa, making them efficient materials for the strengthening of historical masonry buildings in Slovenia.
COBISS.SI-ID: 9109601
A custom made sensor system for measuring the temperature and relative humidity inside the cement-based materials (CBMs) was prepared and its functionality compared with a commercially available ConSensor 2.0 system. The latter reports only a temperature. The results of temperature versus time measurements of both measurement systems are similar. We found that the relative humidity in the samples even after several months did not fall below 80 %. Only after the additional heating of the samples, the relative humidity starts to decrease which was appropriately detected by the home-made measuring system.
COBISS.SI-ID: 8701025
This paper presents the results of cement-based mortars characterizations that were taken from rendered layers of military bunkers in the Rupnik Line. The Rupnik Line was conceived as a part of the fortified defence system protecting the Rapallo Border between the Kingdom of Italy and the Kingdom of Yugoslavia, established in 1920. The bunkers were built between 1938 and 1941, and the renders of various compositions were applied as a camouflage layer that merged the bunkers with the environment. Results of petrographic examination and microstructural and chemical analysis of the samples confirmed that locally available crushed dolomite or limestone sands were used as an aggregate in the mortars. As binders, pure Portland cement or a mixture of cement and ground granulated blast furnace slag were used. The selection of the aggregate and binder type in a particular mortar was based on the colour of the artificial stone produced. All samples with the dolomite aggregate show the presence of alkali-aggregate reactions, dedolomitization of the grains and secondary calcite formation in the cement binder, along with the Mg-Al, Mg-Si and Mg-Al-Si phase formations. In mortar compositions with a high Portland cement content, the presence of delayed ettringite formation was also confirmed.
COBISS.SI-ID: 9112417
This paper investigates the origin of increased strength and water resistance of air lime mortar prepared by Triassic dolomite aggregate when exposed to humid or wet environments. The mortar specimens were exposed to various ageing conditions and analysed using petrographic and scanning electron microscopy equipped with X-ray microanalysis. Parallel to these analyses, X-ray powder diffraction and strength tests were performed on the specimens. It was revealed that reactions associated with the dedolomitisation process of the dolomite grains in the lime binder (hereafter alkali-carbonate reactions or ACRs) are the source of the improved strength and water resistance. An increasingly alkaline environment accelerated the ACRs substantially. Two parallel processes during the ACRs (dedolomitisation and CaCO3 dissolution/reprecipitation) were described in detail. Ageing temperature decisively influenced the kinetics of the dedolomitisation and dictated the path of the CaCO3 dissolution/reprecipitation process. After two years of ageing in a water-saturated environment at 60°C, air lime mortar retained a great deal of its initial mechanical strength, and at 20°C its strength was considerably increased. This somewhat unexpected observation was explained as being a result of microstructural changes and/or phase transitions.
COBISS.SI-ID: 9109089
This paper investigates the process of alkali-carbonate reaction (ACR) in dolomite aggregate concrete in view of its potential as a self-healing process. Samples for the ACR self-healing study were prepared using a cement composite with self-compacting properties in fresh state. The mixture was composed of Portland cement CEM I and typical Slovenian crushed dolomite aggregate in the role of aggregate and stone filler. Samples were subsequently exposed to accelerated testing conditions simulated by 1-M NaOH at 60 °C or deionized water at 60 °C. The conducted research revealed that the complete ACR process was successfully triggered, including the dedolomitization and formation of secondary phases, i.e., CaCO3 called "carbonate halo", Ca-Al-involving phase and some minor phases containing Mg-Al, Mg-Si and/or Mg-Al-Si. Additionally, the "carbonate halo" and Ca-Al-involving phase also precipitated inside purposely preformed cracks in the samples. Smaller cracks were completely filled with the "carbonate halo" and Ca-Al-involving phase. Wider cracks may not have been completely filled with the newly precipitated phases; however, their length and width were also successfully reduced. With filling of the pores and cracks, the mechanical strength of the cement composite was increased substantially due to the ACR self-healing process.
COBISS.SI-ID: 20433155