Use of Spongilites as Pozzolanic Additives in Cement Mortars

In this study, the utilization of two types of spongilites in various addition in cement mortars has been investigated with the purpose of exploring a new application of this natural pozzolans as cement mortar additives. The influence of the addition of spongilites on the physico-mechanical properties, frost-resistance, and microstructure of cement mortars as a function of time was studied. The results revealed that the rising proportion of spongilites in cement mortars causes increase in water retention of mortars, reduction of their bulk density, increase in porosity of mortars due to the growing predominance of capillary pores maintaining sufficient mortars strengths, and slightly increase in the frost-resistance of mortars. After initial tests, partial replacement of cement in fine-grained cement mortars with hitherto unexploited spongilites seems to be very promising. Based on the achieved results, a 20% cement replacement can be recommended as optimal.

THE MICROSTRUCTURE AND PHASE COMPOSITION OF MORTARS FROM THE 17TH CENTURY SACRED BUILDINGS

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.

Ecological Restoration Plasters and Mineral Pigments Designed with Raw Material from the Island of Gavdos

Gavdos is an island of ca. 34 km2 located to the south of Crete, Greece, with a local landscape rich in clay material of remarkable diversity in colour and quality. The limited natural and human-made resources are persistently recycled, forming the built structures of the island and determining the island’s sustainable local tradition. In the framework of this research, areas with clay soil were identified through a geological survey and testimonies of local inhabitants. The studied clay samples were characterized with mineralogical and physicochemical analyses. Two out of ten samples with a clay content higher than 50%, after low-temperature thermal treatment (600 °C and 700 °C), functioned as pozzolanic additives enhancing the performance in resistance to salt decay and plasticity of lime mortars. Seven raw clay samples were used as pigments in lime-based colours and their performance and durability, as assessed with the appropriate laboratory analyses, revealed the existence of stable mineral pigments under UV and visible light irradiation. There is great potential in the exploitation of local raw material from the island of Gavdos for the restoration of the traditional building stock on the island in terms of resource efficiency, environmental impact and preservation of the local identity.

Radiocarbon Dating of Mortars and Charcoals from Novae Bath Complex: Sequential Dissolution of Historical and Experimental Mortar Samples with Pozzolanic Admixture

ABSTRACTCarbonaceous mortars from Novae (Bulgaria) contain local loess, crushed bricks and ceramic dust (pozzolanic materials). The reaction between lime and pozzolanic additives occurs easily and affects the rate and course of leaching reaction of carbonates in orthophosphoric acid during the sample pretreatment for dating. The composition of the Bulgarian mortars does not allow for unambiguous conclusions about chronology, but together with the observations of experimental mortars, gives new guidelines in terms of pozzolanic mortar application for dating. The presented research illustrates the possible reasons of difficulties with obtaining the appropriate portion of gas for radiocarbon (14C) measurement. To verify the relative chronology of legionary baths complex in Novae, the charcoals samples were also dated in addition to the mortar.

Minerālo saistvielu pētījumi Silikātu materiālu institūtā

Parādīti pēdējās desmitgades pētījumi minerālo saistvielu jomā. Pētīta dažādu aktīvo ķīmisko piedevu ietekme uz betona struktūru, mehāniskajām un fizikālajām īpašībām. Novērtēta iegūto betonu korozijas izturība pret sulfātu sāļu šķīdumiem. Pētīta dažādu rūpniecisko blakus produktu – pelnu – kā pucolānu piedevas ietekme uz betona īpašībām.Investigation of Mineral Binders in the Institute of Silicate MaterialsThe influence of natural and artificial pozzolanic and micro-filler additives on the cement paste hydration process, structure, properties was studied. Different additives and chemical compositions were used: micro- and nano-silica, amorphous silicon dioxide synthesized by sol-gel method, glass powder, highly disperse sand, different types of ash. The pozzolanic activity of additives mainly depends on quantity and specific surface area, i. e., the dispersity of active SiO2 and Al2O3. Depending on the pozzolanic activity chemical additives can be used as concrete aggregates or as active additives.The influence of superplasticizer Semflow MC (SP) on microstructure and properties of concrete was investigated. The compressive strength of concrete with SP increased to 154 MPa, corresponding to HPC. The capillary absorption of water and solutions containing sulphate ions into HPC depends on amount of SP. The depth of penetration of solution in the samples decreases consistently by increasing the amount of SP. The formation of crystalline phase during maturation was analysed, and it was found that by increasing testing time the amount of portlandite decreased and calcium hydrosilicate formed. The concrete samples with low W/C ratio, pozzolanic additives and SP up to 2.5 % according mechanical and chemical properties conform to the characteristics of HPC. The investigated concrete has high chemical resistance to solutions containing sulphate ions.Keywords – binders, concrete, pozzolanic additives, ash, concrete corrosion

Effects of Layer-Interface Properties on Mechanical Performance of Concrete Elements Produced by Extrusion-Based 3D-Printing

Interfaces between layers in 3D-printed elements produced by extrusion-based material deposition were investigated on both macro- and micro-scales. On the macro-scale, compression and bend tests were performed on two 3D-printable cement-based compositions (3PCs), namely C1 and C2. The influences of binder composition and time interval between layers on layer-interface strength were critically analyzed. In the context of additive manufacturing, the optimized composition C2, containing pozzolanic additives, exhibited mechanical performance superior to that of the mixture with Portland cement as the sole binder. In particular, Mixture C2 showed a less pronounced decrease in interface tensile strength. Even for time intervals between depositions of two layers as long as 1 day the loss in corresponding flexural strength was below 25%, as compared with C2 specimens tested in the perpendicular direction. In contrast, the decrease in flexural strength measured for C1 specimens amounted to over 90% for the same set of parameters. Higher porosity at the interfaces of the printed concrete layers was identified as the cause for the lower interface strengths of C1. Microscopic observations supported the findings of the macroscopic investigations. While a pronounced recovery (“self-healing”) of the porous, discontinuous interlayers was observed with increasing age for Mixture C2, in case of C1 the filling products grown in the porous interlayer were found to be non-strengthening.

Influence of Pozzolanic Additive on Pore Size Distribution of Lime Mortar

Pozzolanic additives are widely applied as components of cementitious composites as well as mortars based on white lime. They are generally recognized as components improving the durability of resulting material – concrete or mortar. The mechanism responsible for this favorable effect lies in physical and chemical modification of initial binding system. The present paper deals with influence of a pozzolanic additive – ceramic dust (CD) – on pore system of lime – based mortar. The CD was characterized by means of elementary and phase analysis. The range of mortars of varying CD/lime ratio was prepared; their pore size distribution, strength and rate of liquid water and water vapor were determined. The presence of CD caused change in the pore size distribution while the total porosity did not changed significantly. The volume of large pores was reduced and amount of fine pores was increased as consequence of growing CD content. It had positive effect on rate of liquid water transport. Diffusion resistance factor was influenced by the presence of CD towards the lower values; in opposite to the liquid sorptivity the diffusion resistance was controlled by the total porosity. The strength was improved by addition of pozzolanic additive as could be expected. It is in accordance with the reduced volume of capillary pores but obviously the presence of pozzolanic additive in lime converts the binding system to hydraulic and thus the effect of CD on strength cannot be explained just by its influence on pore size distribution.