Influence of cure on the properties of polymer-modified mortars

U radu se opisuje upotreba mikroarmiranog morta s vlaknima od propilena pri sanaciji plašta dimnjaka termoelektrane Šoštanj u Sloveniji. Prikazana je analiza kvalitete ugrađenog mikroarmiranog morta uzimajući u obzir različite uvjete pripreme, ugradnje i njege. Uspoređeni su rezultati ispitivanja fizikalno-mehaničkih svojstava uzoraka uzetih s građevine s uzorcima izrađenim u laboratoriju. Autori zaključuju da je za mortove s dodatkom polimera nužna kratkotrajna mokra njega.The use of propylene-fibre reinforced mortar in the remedy of the chimney stack sheathing at the Šoštanj thermal power plant in Slovenia is presented. The fibre reinforced mortar quality analysis is presented for various preparation, placing and cure conditions. Physicomechanical properties of samples taken from the structure are compared with properties of samples prepared in laboratory. The authors conclude that the short-term wet curing is required for polymer-modified mortars

THE NEW MECHANISM OF FIBRE BONDING IN COMPOSITE MATERIALS

V doktorski disertaciji je obravnavan vpliv dodatkov betonu – mikrosilike, superplastifikatorja in aeranta – na povečanje trdnosti vpetja med cementno malto in pletenico kontinuiranih ogljikovih vlaken. Za preiskavo lastnosti vpetja med pletenico ogljikovih vlaken in različnimi cementnimi maltami so bili uporabljeni rezultati izvlečnih preizkusov, ki smo jih primerjali z rezultati analize mikrostrukture mejnih površin. Eksperimentalni rezultati so potrdili, da je uporaba vseh uporabljenih dodatkov betonu izboljšala kvaliteto vpetja. Najbolj je kvaliteto vpetja med pletenico ogljikovih vlaken in eksperimentalno cementno malto povečala uporaba aeranta. Na podlagi analize rezultatov je bilo ugotovljeno, da lahko zračni mehurčki, ki so posledica delovanja aeranta in so locirani v neposredni bližini zunanjih filamentov pletenice, predstavljajo mehansko oviro, zaradi katere se pri izvleku vlaken občutno poveča trenje na mejni površini. Posledično se povečajo trdnost, togost in žilavost vpetja pletenice ogljikovih vlaken v aerirani malti. V nadaljevanju je v disertaciji prikazana tudi aplikacija novega načina vpetja pletenice ogljikovih vlaken v betonski konstrukciji v primerjavi s klasično rebrasto jekleno armaturo. Po izvedenih upogibnih preizkusih se je izkazalo, da ima vlaknasta armatura številne prednosti pred konvencionalnimi armaturnimi materiali: bistveno stanjšanje prereza (celo do pet krat), majhno maso, možnost poljubnega oblikovanja konstrukcijskih elementov zaradi fleksibilnosti vlaken ter povečano duktilnost in žilavost kompozita.This paper deals with the influence of admixtures – silica fume, superplasticizer and air entraining agent – on the improvement of the bond strength between bundled carbon filaments and cement mortars. Pull-out tests were carried out to examine the bond between carbon-fibre yarn and various cement matrices. An overall microstructural analysis was conducted and correlated with pull-out data. Experimental results showed that all the applied admixtures contributed to improved bonding. The air entraining agent was found to be the most effective in improving the bond strength of the studied carbon-fibre reinforced cement mortar. Air bubbles formed inside the mortar mix as a result of added air entraining agent and the ones formed in the vicinity of the outer filaments of the yarn may provide a mechanical barrier at the interface, leading to a significant increase in interface friction. Additionaly we showed the possibility of using fibrous reinforcement of thin sections compared to a conventional reinforcement with a steel rebars. After carried out bending tests it was proved that the fibrous reinforcement had several advantages over conventional reinforcement materials. The advantages of fiber-reinforced concrete composites are primarily essential thiness of the section (up to five time), low mass, the possibility to arbitrary create elements because of the fiber flexibility and increased ductility and toughness

Influence of cure on the properties of polymer-modified mortars

U radu se opisuje upotreba mikroarmiranog morta s vlaknima od propilena pri sanaciji plašta dimnjaka termoelektrane Šoštanj u Sloveniji. Prikazana je analiza kvalitete ugrađenog mikroarmiranog morta uzimajući u obzir različite uvjete pripreme, ugradnje i njege. Uspoređeni su rezultati ispitivanja fizikalno-mehaničkih svojstava uzoraka uzetih s građevine s uzorcima izrađenimu laboratoriju. Autori zaključuju da je za mortove s dodatkom polimera nužna kratkotrajna mokra njega.The use of propylene-fibre reinforced mortar in the remedy of the chimney stack sheathing at the Šoštanj thermal power plant in Slovenia is presented. The fibre reinforced mortar quality analysis is presented for various preparation, placing and cure conditions. Physicomechanical properties of samples taken from the structure are compared with properties of samples prepared in laboratory. The authors conclude that the short-term wet curing is required for polymer-modified mortars

Durability and Degradation of PVC-P Roofing Membrane—Example of Dynamic Fatigue Testing

This paper presents a study of PVC-P waterproofing membrane Specimens. The Specimens were taken from different segments of a flat roof after a service life of 11 years. The reason for analysing the condition of the Specimens was the apparent degradation of the waterproofing, which no longer guaranteed the watertightness of the roof. The analysis of the performance of the Specimens was based on the control of the mechanical properties, which were compared with the declared values. The mechanical properties of the degraded PVC-P waterproofing membranes with a polyester mesh backing, which are prescribed by the standards, do not usually deviate from the declared properties. This often poses a problem for liability and warranty claims due to the poor quality of the waterproofing membrane. There may be several causes of degradation of PVC-P. For this reason, in this paper, we present the possibility of controlling the properties of PVC-P waterproofing membranes using cyclic dynamic fatigue, microstructure analysis using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the cause of the deterioration of the PVC-P waterproofing membranes is often related to dehydrochlorination of the polymer. However, the deterioration of the mechanical properties of the PVC-P waterproofing membranes can be successfully demonstrated by cyclic dynamic fatigue

Bond improvement in cementitious mortars reinforced with continuous carbon filaments

Najpomembnejši parameter, ki vpliva na lastnosti vlaknastih cementnih kompozitov, je kvaliteta vezi v stični coni med matrico in vlakni. Članek obravnava vpliv mikrosilike in superplastifikatorja na povečanje trdnosti stika med cementno malto in snopičem kontinuiranih ogljikovih vlaken. Analiza mikrostrukture z elektronskim vrstičnim mikroskopom je pokazala, da je dodatek mikrosilike zmanjšal poroznost in količino CH kristalov in tako utrdil stično cono in ojačal vpetje vlaken. Dodatek superplastifikatorja je sicer izboljšal obdelovalnost sveže malte, kar pa ni bistveno vplivalo na izboljšanje kvalitete vpetja. Trdnost stika je bila kvantitativno ovrednotena z rezultati izvlečnih testov,ki so pokazali, da se z dodatkom kombinacije mikrosilike in superplastifikatorja doseže največje izboljšanje stika med cementno matrico in ogljikovimi vlakni.Among various parameters that influence the properties of the composite, the bond between the cementitious matrix and the fibres is the most important one. This paper investigates the influence of admixtures - silica fume and superplasticizer - on the improvement of the bond strength between bundled carbon filaments and cementitious mortars. An overall microstructural analysis has shown that the addition of silica fume strengthen the interfacial transition zone by both the reduction of its porosity and the consumption of CH crystals. The addition of a superplasticizer increased the workability of fresh mortars but the improvement of the bond strength was not significant. Fibre-bundle pull-out tests were caried out to confirm the effectiveness of the admixtures to improve the bond strength. Based on the resulting load-displacement curves, the combination of silica fume and superplasticizer were found to be the most effective in improving the bond strength of the composite

Freeze-thaw durability of concrete with recycle tire rubber and chemical admixtures

Odpadne gume in elektrofiltrski pepel se zbirajo v velikih količinah, zato njihova uporaba prispeva k reševanju problema onesnaževanja okolja. V članku je predstavljena receptura betonske mešanice z dodatkom reciklirane gume kot nadomestkom dela agregata in z elektrofiltrskim pepelom kot delnim nadomestkom cementa. Tak beton ustreza trdnostnemu razredu C12/15 in je primeren za izdelavo podložnih betonov. Na laboratorijskih preizkušancih so bili analizirani vplivi reciklirane gume in elektrofiltrskega pepela na notranjo odpornost betona proti zmrzovanju in tajanju. Ugotovljeno je bilo, daje za doseganje notranje odpornosti betona potrebno povečanje prostornine por z dodatkom aeranta.Scrap tires and fly ash are being generated and accumulated in large volumes causing an increasing threat to the environment. There are mechanical, environmental and economic reasons to include recycled rubber and fly ash in concrete mixture. The concrete mixture with recycled rubber and fly ash is presented. Concrete used in foundations of non-load bearing structures should be a minimum strength classification of C12/15. In the paper, the freeze-thaw resistance of rubber included concrete with fly ash were investigated. Rubber included concrete is not freeze-thaw resistant, without entrained air

Hardening of concrete with a planned delayed ettringite formation

Delayed ettringite formation (DEF) in cementitious materials is widely considered as a harmful chemical reaction that causes extensive damages in hardened concrete. However, preventative measures and possible improvements in general are not extensively studied and require further attention. In this study was presented an investigation into a type of controlled DEF in places of finely dispersed crystallisation nuclei and provide evidence that the process may improve compressive strength of cementitious materials. The Alkali-Silica Reaction (ASR) in hydrated concrete was achieved with the addition of fly ash and was further accelerated with the Dugganćs test. Achieved strengths and monitoring of microstructure development conducted with electronic microscopy revealed that growth of ettringite crystals in the nuclei led to harmless internal compressive stresses, expansion of hydrated concrete and overall strengthening of the concrete matrix

Bond improvement in cementitious mortars reinforced with continuous carbon filaments

Among various parameters that influence the properties of the composite, the bond between the cementitious matrix and the fibres is the most important one. This paper investigates the influence of admixtures - silica fume, superplasticizer and air entraining agent - on the improvement of the bond between bundled carbon filaments and cementitious mortars. An overall microstructural analysis has shown that the addition of silica fume strengthen the interfacial transition zone by both the reduction of its porosity and the consumption of CH crystals. The addition of a superplasticizer increased the workability of fresh mortars, but the bond improvement was insignificant. The application of the air entraining agent caused the formation of air bubbles inside the mortar matrix. Air bubbles formed in the vicinity of the multifilament yarn were found to provide mechanical anchoring for fibres leading to a significant increase in interface friction. Fibre-bundle pullout tests were carried out to confirm the effectiveness of the admixtures to improve the interface bonding. Based on the resulting load-displacement curves, air entraining agent was found to be most effective in enhancing the bonding characteristics of the cementitious composite