Comparison of Pozzolanic Additives for Normal and High Strength Concrete

Microsilica is widely recognized as a “benchmark” for pozzolanic products. Although microsilica is an industrial byproduct, it has recently become very expensive. Four different pozzolanic additives were compared by the authors of this study. Two of the additives were commercially available products – microsilica by Elkem and Centrilit NC by MC Bauchemie. The other two additives were produced under laboratory conditions. Both of them were clay-based materials. Compressive strength was determined after 7, 28 and 155 days. The objective of this research was to determine alternatives to microsilica and evaluate pozzolanic additives performance in normal and high-strength concrete

Percolation experiment across a 10-year-old interface between Opalinus Clay and Portland concrete

An interface sample between Portland concrete and Opalinus Clay with a contact time of 10 years recovered from a field experiment was investigated by SEM-EDX and X-ray CT. The concrete side showed a large chloride ingress from the claystone alongside a decalcification and an opening of the porosity. Additional XRD, TGA and leaching experiments of the concrete at few centimetres (∼5 cm) away from the interface confirmed the chloride ingress. The interface was then subjected to a long-term percolation experiment accompanied with repeated X-ray CT-scans. Injection of synthetic claystone pore water proceeded into the claystone-part of the sample, and through the concrete part, whereby the outflow was continuously sampled. The bedding joints that were partially desaturated rapidly saturated, while hydraulic conductivity steadily decreased to values similar to unaltered claystone. The analysis of the exfiltrating aliquots shed light on the advective/diffusive properties of water transport and multi-component solute transport

The Effect of Heat Treatment on the Properties of Ultra High Strength Concrete

The influence of heat treatment during curing process of ultra high strength concrete (UHSC) was researched. Four different heat treatment temperatures ranging from 50 to 200 °C were studied and compared to the reference temperature regime (20 °C).  Two series of heat treatment were applied: (a) at the early age of UHSC (3 days) and (b) after 27 days of standard curing regime in water at 20 °C. Concrete compressive strength was tested at the early age (4 days) and at the age of 28 days. The water absorption and water penetration under pressure were tested for heat treated and untreated UHSC specimens. SEM and XRD investigations of the studied samples were performed. UHSC with the strength of 123 MPa at the age of 28 days was tested at the standard curing conditions. Results indicate that early age curing at elevated temperature increases early compressive strength from 123 to 189% while at the age of 28 days the compressive strength was only 95 to 117% from reference and depends on the heat treatment regime. The heat treatment of UHSC at the age of 27 days was beneficial with regard to the strength development. Heat-treated UHSC provided compressive strength gain from 112 to 124% from reference. The water absorption for all UHSC specimens was from 2.6 to 3.2 wt.% and it was not affected by the heat treatment. The calcite was detected with XRD in heat treated UHSC samples which indicates the carbonization of Portlandite. This could explain the strength gain of heat-treated samples and the reason for slow compressive strength increase in the case of early heat treatment application. SEM images reveal dense structure and unreacted silica fume particles. The early heat treatment initiated high early strength but the strength of concrete reduced at the age of 28 days comparing to the early strength; therefore late heat application was beneficial for strength gain of the UHSC

Influence of different fibers on the change of pore pressure of self-consolidating concrete exposed to fire

The focus of this paper is given to investigate the effect of different fibers on the pore pressure of fiber reinforced self-consolidating concrete under fire. The investigation on the pore pressure-time and temperature relationships at different depths of fiber reinforced self-consolidating concrete beams was carried out. The results indicated that micro PP fiber is more effective in mitigating the pore pressure than macro PP fiber and steel fiber. The composed use of steel fiber, micro PP fiber and macro PP fiber showed clear positive hybrid effect on the pore pressure reduction near the beam bottom subjected to fire. Compared to the effect of macro PP fiber with high dosages, the effect of micro PP fiber with low fiber contents on the pore pressure reduction is much stronger. The significant factor for reduction of pore pressure depends mainly on the number of PP fibers and not only on the fiber content. An empirical formula was proposed to predict the relative maximum pore pressure of fiber reinforced self-consolidating concrete exposed to fire by considering the moisture content, compressive strength and various fibers. The suggested model corresponds well with the experimental results of other research and tends to prove that the micro PP fiber can be the vital component for reduction in pore pressure, temperature as well spalling of concrete.National Natural Science Foundation of China (Grant: 51121005), DUT and Fundaçãopara a Ciência e a Tecnologia (SFRH/BPD/22680/2005), the FEDER Funds through “Programa Operacional Factores de Competitividade - COMPETE" and by Portuguese Funds through FCT-within the Projects PEst-CMAT/UI0013/2011 and PTDC/MAT/112273/2009

Testing superabsorbent polymer (SAP) sorption properties prior to implementation in concrete: results of a RILEM Round-Robin Test

This article presents the results of a round-robin test performed by 13 international research groups in the framework of the activities of the RILEM Technical Committee 260 RSC "Recommendations for use of superabsorbent polymers in concrete construction''. Two commercially available superabsorbent polymers (SAP) with different chemical compositions and gradings were tested in terms of their kinetics of absorption in different media; demineralized water, cement filtrate solution with a particular cement distributed to every participant and a local cement chosen by the participant. Two absorption test methods were considered; the tea-bag method and the filtration method. The absorption capacity was evaluated as a function of time. The results showed correspondence in behaviour of the SAPs among all participants, but also between the two test methods, even though high scatter was observed at early minutes of testing after immersion. The tea-bag method proved to be more practical in terms of time dependent study, whereby the filtration method showed less variation in the absorption capacity after 24 h. However, absorption followed by intrinsic, ionmediated desorption of a specific SAP sample in the course of time was not detected by the filtration method. This SAP-specific characteristic was only displayed by the tea-bag method. This demonstrates the practical applicability of both test methods, each one having their own strengths and weaknesses at distinct testing times

Neutron imaging of cadmium sorption and transport in porous rocks

Understanding fluid flow in rocks is crucial to quantify many natural processes such as ground water flow and naturally triggered seismicity, as well as engineering questions such as displacement of contaminants, the eligibility of subsurface waste storage, geothermal energy usage, oil and gas recovery and artificially induced seismicity. Two key parameters that control the variability of fluid flow and the movement of dissolved chemical species are (i) the local hydraulic conductivity, and (ii) the local sorption properties of the dissolved chemical species by the solid matrix. These parameters can be constrained through tomography imaging of rock samples subjected to fluid injection under constrained flow rate and pressure. The neutron imaging technique is ideal to explore fluid localization in porous materials due to the high but variable sensitivity of neutrons to the different hydrogen isotopes. However, until recently, this technique was underused in geology because of its large acquisition time. With the improved acquisition times of newly set-up neutron beamlines, it has become easier to study fluid flow. In the current set of experiments, we demonstrate the feasibility of in-situ 2D and 3D time-lapse neutron imaging of fluid and pollutant percolation in rocks, in particular that of cadmium salt. Cadmium is a hazardous compound that is found in many electronic devices, including batteries and is a common contaminant in soil and groundwater. It also exhibits higher contrast in neutron attenuation with respect to heavy water, and is therefore an ideal tracer. Time-lapse 2D radiographies and 3D neutron tomographies of the samples were acquired on two neutron beamlines (ILL, France and SINQ, Switzerland). We performed two sets of experiments, imbibition and injection experiments, where we imaged in-situ flow properties, such as local permeability and interactions between cadmium and the solid rock matrix. Our results indicate that even within these cm-scale porous rocks, cadmium transport follows preferential pathways, and locally interacts within the limestone samples. Our results demonstrate that the use of neutron imaging provides additional insights on subsurface transport of pollutants.Applied Geophysics and Petrophysic

Management Problems of Persistant Organic Pollutants in Latvia

Bakalaura darba „Noturīgo organisko piesārņotāju pārvaldes problēmas Latvijā” mērķis ir analizēt Latvijā spēkā esošajos normatīvos aktus un pārvaldes modeļus noturīgo organisko piesārņotāju, kuri ir vieni no bīstamākajiem piesārņotājiem, kas cilvēku darbības rezultātā nonāk vidē, jomā, kā arī izstrādāt nepilnību risinājumu variantus un iespējamus jaunus pārvaldes modeļus. Analīze parādīja, ka normatīvie akti ir nepilnīgi. Tas traucē starptautisko saistību izpildi, it īpaši galveno definīciju un pieļaujamo koncentrāciju ziņā. Tāpat parādījās arī pārvaldes mehānisma vairāku posmu neefektivitāte. Darba galvenie secinājumi: jāveic normatīvo aktu pilnveidošana, lai varētu izpildīt Stokholmas konvencijā paredzētās saistības, kā arī jāreorganizē noturīgos organiskos piesārņotājus saturošu iekārtu savākšanas uzglabāšanas un iznīcināšanas shēma.The purpose of Bachelor Thesis is to analyze legal acts considering persistent organic pollutants that are binding for Latvia and give possible solutions for existing imperfections and suggest new possible management models. The analysis showed that the existing legislation contains some disadvantages that prohibits fulfillment of the Stockholm Convention. The most imperfections concern the main definitions and acceptable concentrations. Also much inefficiency was discovered in the current management model. Main conclusions of the Bachelor Thesis: it is urgently necessary to improve the existing legislation and reorganize collection, storage and disposal of machinery containing persistent organic pollutants

Management Problems of Persistant Organic Pollutants in Latvia

Bakalaura darba „Noturīgo organisko piesārņotāju pārvaldes problēmas Latvijā” mērķis ir analizēt Latvijā spēkā esošajos normatīvos aktus un pārvaldes modeļus noturīgo organisko piesārņotāju, kuri ir vieni no bīstamākajiem piesārņotājiem, kas cilvēku darbības rezultātā nonāk vidē, jomā, kā arī izstrādāt nepilnību risinājumu variantus un iespējamus jaunus pārvaldes modeļus. Analīze parādīja, ka normatīvie akti ir nepilnīgi. Tas traucē starptautisko saistību izpildi, it īpaši galveno definīciju un pieļaujamo koncentrāciju ziņā. Tāpat parādījās arī pārvaldes mehānisma vairāku posmu neefektivitāte. Darba galvenie secinājumi: jāveic normatīvo aktu pilnveidošana, lai varētu izpildīt Stokholmas konvencijā paredzētās saistības, kā arī jāreorganizē noturīgos organiskos piesārņotājus saturošu iekārtu savākšanas uzglabāšanas un iznīcināšanas shēma.The purpose of Bachelor Thesis is to analyze legal acts considering persistent organic pollutants that are binding for Latvia and give possible solutions for existing imperfections and suggest new possible management models. The analysis showed that the existing legislation contains some disadvantages that prohibits fulfillment of the Stockholm Convention. The most imperfections concern the main definitions and acceptable concentrations. Also much inefficiency was discovered in the current management model. Main conclusions of the Bachelor Thesis: it is urgently necessary to improve the existing legislation and reorganize collection, storage and disposal of machinery containing persistent organic pollutants

Distribution of trace elements in sediments of Lake Liepaja

Darbā novērtēts vairāku mikroelementu (Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg un Pb) sadalījums Liepājas ezera sedimentos. Telpiskais elementu sadalījums ir samērā heterogēns, kas norāda uz vairākiem iespējamiem mikroelementu izcelsmes avotiem. Sedimenti tika sadalīti frakcijās ar sekojošiem daļiņu izmēriem: 100 μm, 80 μm, 63 μm, 50 μm un <50 μm. Visaugstākās koncentrācijas visiem elementiem tika konstatētas sedimentu frakcijās ar daļiņu izmēriem 63 un 50 μm. Sedimentu kvalitāte un piesārņotības pakāpe tika novērtēta izmantojot ģeoakumulācijas indeksu, bagātinātības faktoru, piesārņojuma slodzes indeksu un koncentrēšanas faktoru, kas parādīja, ka sedimenti visās frakcijās nav piesārņoti ar Mn, Ti, Ni, un V, savukārt ir piesārņoti ar Pb, Zn, Cu un Cr. Piesārņotības pakāpi attiecībā uz Cd un Hg no iegūtajiem rezultātiem nebija iespējams viennozīmīgi novērtēt.Spatial and statistical distribution of heavy metals (Ti, Cr, Mn, Fe, Ni, Cu, Zn, As, Cd, Hg and Pb) in sediments of Lake Liepaja was assessed. Spatial distribution of heavy metals showed heterogeneous dispension in the lake, which suggests the existance of different pollution sources. Sediments were separated into following fractions by particle size: 100 μm, 80 μm, 63 μm, 50 μm and <50 μm Maximum concentrations for all analysed elements were observed in the sediment fractions with particle size of 63 and 50 μm. Sediment quality was characterized by the geoaccumulation index and enrichment factor that show unpolluted level of Mn, Ti, Ni, and V in all fractions and polluted character concerning to Pb, Zn, Cu and Cr. Indefinite pollution status refers to Cd and Hg