Widespread opinion holds that calcareous rocks have limited suitability for use in the production
 

 of aggregates and stone products having adequate frost resistance. However, some of the rocks, in
 

 particular those from earlier geological periods, provide a promising alternative to silicate rocks.
 

 The paper presents results of the analysis of Devonian carbonate rock originating from two selected
 

 mines in the Swietokrzyskie region. The examined mines extract limestone from two different
 

 deposits of the same age. The rock samples are collected from beds lying at different depths, distinct
 

 in texture and color in macroscopic examination. It was found that despite the changes in bulk density,
 

 porosity and absorption, all the examined samples were frost resistant.
 

 Using the Differential Analysis of Volumetric Strain method, the content of ice formed in the pore
 

 spaces was determined. In addition, the ratio of the content of water capable of freezing to the total
 

 pore volume, and the total amount of water absorbed due to capillary action in rock samples soaked
 

 in water, were analyzed. In all cases, it was revealed that the destructive action of freezing water was
 

 weakened due to a relatively low content of water capable of freezing and a substantial volume of
 

 pores that are not filled with water in capillary absorption.
 

 It is extremely important to be able to classify the available rock material. The generally adopted
 

 methods, including absorptivity tests, do not allow for precise categorization. In the investigations,

the authors focused on the analysis of the basic factors that are decisive for rock durability, including bulk density, pore filling level and volume absorption. The authors do not correspond compressive

strength and resistance to abrasion as this will be the subject of further research.

The technology of recycling with foamed bitumen is a new technology of road rehabilitation. Due to the climatic conditions in the Central European countries, road pavement structure should be moisture and frost resistant. Because of its specific production conditions, this is especially important for pavements rehabilitation with the cold recycling technology. Determining the physical and mechanical properties, as well as moisture and frost resistance, depends on binder and filler contents. They are the key elements before its use for road building. The tests presented here have been performed on mineral recycled base mixes with foamed bitumen. The material from the existing layers was used. The content of bitumen binder amounted to 2.0%, 2.5%, 3.0% and 3.5%, while that of cement to 1.0%, 1.5%, 2.0%, 2.5%. The results were subject to the optimization process. This allowed to state that with the use of 2.5% foamed bitumen and 2.0% of cement, the base had the required properties, as well as the moisture and frost resistance.

The paper concerns the use of limit value of siliceous fly ash content in concrete structures, with the application of various types of cements - based on the current standards and taking into consideration the requirements concerning current exposure classes. The conclusions were based on a review of literature, the results of scientific research, conclusions from expert opinions and buildings and structures supervision reports. In summary, it has been concluded that the use of limit content of siliceous fly ashes may result in negative changes in the properties of composites, which should be ruled out or confirmed by appropriate tests, taking into account the precisely defined composition of concrete, cement and the applied additives and admixtures. It has been emphasised that the problem concerns composites with the increased and limit values of fly ash content, especially as regards cements with the lowered content of clinker and high content of additives and admixtures (affecting the physical and mechanical properties of cement composites). Attention has been drawn to the need to modify the exposure classes, to focus on the requirements concerning the properties of concrete and not the composition - in order to achieve the expected durability.

In the latest period hundreds of concrete viaducts were built in Poland within a short time range. The cases of destruction of concrete road viaducts described by the author in the article concern in the construction of such structures in various parts of our country, such as central regions of Poland, Warmia-Masuria, south – east - a total of about 30 objects. The occurring phenomenon is related to the micro cracks of the cement matrix which are not visible on the surface of the elements and become visible only after the cyclic freezing process as a result of the standard F150 frost resistance test, the so-called the standard method according to Annex N to the PN-B-06265: 2018 standard. The destruction took an unprecedented course and aroused much discussion in the scientific community. This article summarizes this discussion and indicates the root cause of the destruction.

The effect of the air-entraining agent on properties of mortar mixtures as well as on the compressive strength of hardened mortars was the objective of this study. Such mortars contain a certain amount of evenly spread closed air-voids pores with dimensions of 0.02-0.05 mm. On the one hand, the presence of a large volume of such air bubbles results in the reduction of mechanical properties of mortar. On the other hand, the use of this technological approach improves rheological properties of mortar mixture. The effect of the air entrainment on the flow, density, volume of entrained air of mortar mixture and compressive strength of hardened mortar was established. Obtained results show substantial increasing in the mortar flow at cement to sand ratio 1:2 by 1.8 times. The further decrease of C:S ratio results in a slight increase of the flow and even negligible its decrease at C:S = 1:4 compared to the reference mortar. The increase of the volume of entrained air results in the decrease of the density and compressive strength of mortar, but improve the resistance to freezing/thawing cycles. The results of this study can be a guide for mortar mix design to choose the most appropriate mix proportion to produce economically efficient mortars.

For the decreasing of too high air volume in SCC, application of anti-foaming admixture (AFA) is proposed. In effect, AFA is increasing mix flow diameter and decreasing the flow time. Moreover, the workability loss is lower. In case of mix incorporating AFA, their high fluidity do not generate segregation of the mix, which is possible in case of SCC incorporating only SP. The effect of AFA application on the compressive strength depends on the proportions between SP and AFA. AFA has not a negative influence on the freeze-proof properties of the tested concrete. The advisable influence of AFA on porosity characteristic of SCC is proved by research results according to EN 480-11 code.

The article discusses the physical and chemical mechanisms of the carbonation phenomenon itself, as well as points out the synergistic effect of frost destruction and concrete carbonation on reinforced concrete elements. Examples of structural damage from engineering practice in the diagnosis of reinforced concrete structures are presented. Two cases of frost and carbonation damage of precast reinforced concrete elements are analyzed. It was noted that the most common cause of damage to concrete structures is the lack of frost resistance. Carbonation of concrete leads to deprivation of the protective properties of the concrete lagging against the reinforcing steel. The examples cited include precast elements that, for technical reasons, had a relatively small lagging thickness. The first one relates to the thin walled elevation elements, which are exploited during 60 years and the second relates to the energetic poles with very advanced concrete corrosion damage. The examples given of corrosion of concrete and reinforcement of elements indicate that synergistic environmental interactions can intensify the destruction of elements.

The article presents the results of experimental studies of the influence of granite dust on the properties and durability of concrete. The use of industrial waste – granite dust, in the processing of granite into crushed stone, at the same time allows the rational use of natural resources and solve environmental problems. The possibility of improving the construction and technical properties of concrete filled with granite dust is considered. Experimental-statistical models of technological and physical-mechanical properties of concretes are presented and analyzed, ways of their improvement are shown. The complex of strength properties, water absorption, frost resistance, and durability of such concrete have been studied. The studied concrete are characterized by a more intensive set of strength and obtaining mixtures of “sticky” consistency. Due to the partial replacement of sand by granite dust, the microstructure of the cement matrix is compacted, which is the main reason for reducing porosity and increasing the durability of structures based on the proposed concrete.