Mechanical properties of self-compacting concrete with different mineral aditives after high temperature exposure

This paper presents an experimental research on the performance of high-strength self-compacting concrete (SCC) with different mineral additives after exposure to high temperature of up to 600°C. For this purpose, four SCC mixtures were studied: one reference and three mixtures where the Portland cement was replaced with mineral additive (fly ash, metakaolin and limestone) in certain proportions. After natural cooling in the furnace, compressive strength and static modulus of elasticity were determined and compared to results obtained from other studies and those provided in EN 1992-1-2 and EN 1994-1-2 for normal-vibrated concrete. Additionally, in order to characterize the damage of the specimens caused by high temperatures, AE parameters during compression test of heated and unheated specimens were also obtained

Monitoring of Concrete Hardening Using Acousto-Ultrasonic Method

In civil engineering practice there is often the need for estimation of compressive strength of concrete during construction process and for that purpose different testing methods have been proposed. This paper deals with application of acousto-ultrasonic (AU) measurement method for monitoring of strength development process in concrete and presents outcomes of an experimental investigation on six concrete mixtures prepared with two types of cement and three different w/c ratios. Experimental work was conducted in Laboratory for materials testing at Civil Engineering Faculty in Zagreb

Učinci razine zaslanjenosti vode za navodnjavanje na produktivnost boba (Vicia faba L.)

In Mediterranean region where seawater intrudes porous karst matrix and salinizes soil and water resources, water used for the irrigation of crops is frequently of inadequate quality. Measuring the productivity of horticultural crops under saline conditions helps to determine whether and when to irrigate crops if water is saline, thus balance between crop water and salt stress. A greenhouse pot experiment was set to study the effects of saline irrigation water on faba bean (Vicia faba L.) biomass and yield parameters. NaCl salinity was applied in a nutrient solution as follows: NaCl0 as control (nutrient solution without added NaCl), NaCl50 (control + 50 mM NaCl), and NaCl100 (control + 100 mM NaCl). Five weeks after salinity treatment started, plant height (cm), number of lateral branches per plant, number of pods and seeds per plant, shoot weight (g), pod weight (g) and seed weight (g) were determined. Compared to control, increased irrigation water salinity statistically significantly decreased measured parameters (P<0.01), except for number of branches and pods. Faba bean productivity decreased proportionally to the irrigation water salinity level, suggesting that optimal saline agriculture management strategy can be to allow for the acceptable yield loss in order to avoid plant water stress.Na području Mediterana, gdje dolazi do prodora morske vode kroz porozni krški materijal i zaslanjivanja tala i vodnih resursa, voda koja se koristi za navodnjavanje usjeva često nije odgovarajuće kakvoće. Mjerenje produktivnosti hortikulturnih usjeva u zaslanjenim uvjetima pomaže odrediti može li se navodnjavati zaslanjenom vodom i kada, kako bi se pronašla ravnoteža između vodnog stresa usjeva i stresa soli. Postavljen je pokus u loncima u plasteniku kako bi se istražili učinci zaslanjene vode za navodnjavanje na biomasu i parametre prinosa boba (Vicia faba L.). NaCl sol je primijenjena u hranjivoj otopini kako slijedi: NaCl0 kao kontrola (hranjiva otopina bez dodanog NaCl), NaCl50 (kontrola + 50 mM NaCl), i NaCl100 (kontrola + 100 mM NaCl). Pet tjedana nakon početka tretmana zaslanjenom vodom, izmjerena je visina biljaka (cm), određen broj bočnih izdanaka, mahuna i sjemenki po biljci, masa nadzemnog dijela biljke (g), masa mahune (g) i masa sjemena (g). U usporedbi s kontrolom, povećana zaslanjenost vode za navodnjavanje statistički je značajno smanjila mjerene parametre (P<0.01), osim broja izdanaka i mahuna. Produktivnost boba smanjila se proporcionalno razini zaslanjenosti vode za navodnjavanje, sugerirajući da optimalna strategija poljoprivrednog gospodarenja u zaslanjenim uvjetima može biti dozvoljavanje prihvatljivog gubitka prinosa kako bi se izbjegao vodni stres usjeva

Agricultural Management Strategies for Countering Drought Conditions in Eastern Croatia

The occurrence of drought periods which last for several months is becoming increasingly frequent, even in regions which have not encountered them before. Agricultural production is very sensitive to drought, and in areas where such conditions were rather unexpected, it is also unprepared for limited water management. As an example, in the area of the Biđ-Bosut field located in eastern Croatia, a significant change in the agricultural soil water regime is noticed during a long-term study (2003–2018). From 2003 to 2018, the groundwater level at 4 m below the soil surface showed a decreasing trend of 6–10 cm annually, while this negative trend was even more prominent from 2014 to 2018 (18–71 cm annually). Furthermore, water level in a groundwater aquifer at 15 m below the soil surface showed a decreasing trend of 26–77 cm during 2015–2018. In accordance with the obtained results, this study proposes certain agro-hydrotechnical strategies which can be used in agricultural production to alleviate the effects of drought period. Although these management strategies are primarily described on an eastern continental Croatia example, they can also be applied in all agricultural areas with similar agroecological conditions

Strawberry Growth and Fruit Yield in a Saline Environment

Up to 20% of irrigated arable land in arid and semi-arid regions worldwide is salt-affected. The problem of salt-affected soils is also present in the Croatian Mediterranean coastal region where seawater intrudes through porous media into calcareous aquifers, mixes with freshwater and salinizes both ground and surface waters. Climatic conditions enable continuous growing of several crops throughout a year, but increasing demand for irrigation water forces the growers to utilize water of poor quality. In 2005, the effect of rising salinity levels (control, 4, 6, and 8 dS m-1) on strawberry vegetative growth and fruit yield was studied in a greenhouse experiment. Salinity treatments had a negative effect on total fresh fruit yield (29-59%), total number of fruits (24-45%), fruit size, as well as on the number of runners (23-86%) and the length of the longest runner (1.3-2.6 times). Furthermore, NaCl salinity stress accelerated leaf senescence and reduced the strawberry growing period by 12-22 days

Ultrazvučna karakterizacija cementnih kompozita tijekom hidratacije

Ultrasonic measurements used to monitor the hydration of cement based materials are becoming an important tool in the quality assurance in production. Also, using these methods can be cost benefit for the construction companies because they can provide information about evolution of material properties in real time. In this paper ultrasonic testing is used to characterize a hydration process of cement paste. A technique is based on the system for measuring the ultrasonic pulse velocity (UPV). To obtain more information about wave propagation characteristics the technique of acoustic emission (AE) is also used. Entire waveform of the signal is recorded. AE parameters are extracted from the signal and used to characterize different processes in cement paste during hydration. An analysis is performed on cement pastes made with different water-cement ratios. Ultrasonic wave parameters are compared to the initial and final setting time using the Vicat needle test and compressive strength development.Korištenje ultrazvučnih mjerenja za praćenje hidratacije materijala na bazi cementa postaje važan alat osiguranja kvalitete u proizvodnji. Također, korištenje tih metoda može biti ekonomski isplativo za izvođačke tvrtke jer omogućavaju trenutno dobivanje informacija o razvoju svojstava materijala. U ovom radu ispitivanje ultrazvukom je primijenjeno za karakterizaciju procesa hidratacije cementne paste. Metoda mjerenja temeljena je na sustavu za mjerenje brzine ultrazvučnog impulsa (UPV). Kako bi se dobilo više informacija o svojstvima širenja valova korištena je i metoda akustične emisije (AE). Cijeli valni zapis je sniman te su iz signala izračunati parametri akustične emisije koji su korišteni za karakterizaciju različitih procesa u cementnoj pasti tijekom hidratacije. Analiza je provedena na cementnim pastama izrađenim s različitim vodo-cementnim omjerima. Parametri ultrazvučnih valova uspoređeni su s početkom i krajem vezanja dobivenim Vicatovom iglom i razvojem tlačne čvrstoće

Modifications of dolomite-based self-compacting concrete properties using mineral additives

U radu su opisana istraživanja svojstava samozbijajućih (SCC) betona spravljenih s dolomitnim filerom i materijalima koji posjeduju pucolanska svojstva, letećim pepelom i metakaolinom, kao zamjena za cement u različitim postotcima. Projektirano je sedam mješavina sa jednakim omjerom voda/prah i jednakim udjelom praškastog materijala. Ispitivanja svježih svojstava su se sastojala od ispitivanja rasprostiranja slijeganjem, ispitivanja L-kutijom i ispitivanja segregacije, a u očvrsnulom stanju je ispitana tlačna čvrstoća i modul elastičnosti za različite starosti betona od 2, 7, 14, 28 i 365 dana. Kako bi se pratila aktivnost dodanih mineralnih dodataka u betonske mješavine, ispitana je i toplina hidratacije. Dobiveni rezultati pokazuju da dodatak letećeg pepela u mješavinama poboljšava svojstva obradljivosti, dok uporaba metakaolina poboljšava mehanička svojstva. Usporena pucolanska aktivnost letećeg pepela usporava razvoj tlačne čvrstoće, ali rezultati dobiveni ispitivanjem nakon godinu dana starosti pokazuju da konačna čvrstoća betona s dodatkom letećeg pepela nije manja u odnosu na referentnu mješavinu.This paper addresses fresh and hardening properties of self compacting concretes (SCC) made with dolomite filler and pozzolanic materials, fly ash and matekaolin as cement replacement in different amounts. For this study, seven mixtures were prepared with a constant water-to-powder ratio and powder content. Fresh SCC properties were assessed by means of slump flow, L-box and sieve segregation test, while hardened properties were evaluated by means of compressive strength and modulus of elasticity at ages of 2, 7, 14, 28 and 365 days. In addition, the activity of mineral additives was assessed by heat of hydration measurement. Obtained results showed that mixtures containing fly ash exhibited better performance concerning workability properties needed for SCC, while cement replacement with metakaolin enhanced the mechanical properties. Slower pozzolanic activity of fly ash reflected in slower strength development, but ultimate strength obtained at the age of 365 days was not reduced by the presence of fly ash