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

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

Kūdras izmantošana siltumizolācijas materiālu ražošanā. Aktivētās kūdras saistvielas iegūšana un tās izmantošana kūdras-kokskaidu siltumizolācijas kompozītos

Par aktuālu problēmu mūsdienās ir kļuvusi energoefektivitātes nodrošināšana ēkām un būvēm. Latvijas siltumizolācijas būvmateriālu tirgus mūsdienās lielākoties ir pārstāvēts ar ārzemēs ražotiem siltumizolācijas materiāliem un to izejvielām. Pētījuma gaitā tika apskatīt vietējie resursi un izejvielas, kas var tikt izmantoti siltumizolācijas materiālu ražošanā. Latvijas dabas bagātība ar lielu potenciālu siltumizolācijas būvmateriālu ražošanā ir kūdra, šī resursa aptuvenie apjomi valstī ir 1.7 miljardi tonnu, aizņemot apmēram 10% no valsts teritorijas. Latvijā plaši attīstīta ir kokapstrādes rūpniecība, kuras blakusprodukts – kokskaidas tika izmantots pētījuma gaitā kā pildviela kūdras-kokskaidu siltumizolācijas kompozītmateriālā. Šī darba mērķis ir praktiski iegūt aktivētās kūdras masu ar saistvielas īpašībām un radīt ekoloģiski tīru siltumizolācijas materiālu ar 100% vietējo izejvielu izmantošanu. Ar kūdras aktivāciju pirmkārt saprot dažādu kūdras sastāvdaļu izteiktāku darbību dažādos procesos, esošo raksturīgu īpašību paaugstināšanos un jaunu īpašību atklāšanu. Pastāv vairāki kūdras aktivācijas veidi, tostarp: mehāniskā, termiskā, ķīmiskā un kombinētā. Pētījuma ietvaros tika izmantota kūdras mehāniski-termiskā aktivācija ūdens vidē ložu planetārajās dzirnavās. Dažādu materiālu īpašības ir tiešā veidā saistītas ar to sastāvdaļu un izejvielu īpašībām. Izejvielu kvalitātes paaugstināšana ļauj ne tikai uzlabot izstrādājumu kvalitāti, bet arī lietderīgāk izmantot dabas resursus. Risinot cilvēces globālās problēmas, katra atsevišķa resursa lietderīgāka izmantošana kļūst arvien aktuālāka. Kūdras aktivācijas režīmu novērtēšanai tika izgatavoti un pārbaudīti spiedē kūdras-kokskaidu kompozītmateriāla paraugi. Iegūtā aktivētā kūdras masas daļiņu izmēru un homogenitātes izmaiņas atkarībā no aktivācijas laika tika vizuāli novērtētas izmantojot elektrisko mikroskopu. Pētījuma gaitā tika praktiski iegūti dažāda tipa siltumizolācijas materiāli un aktivētās kūdras masa ar saistvielas īpašībām, kas var tikt plaši izmantota arī citu materiālu radīšanā. Iegūtās vielas un materiāli: -Aktivētās kūdras masa ar saistvielas īpašībām, var tikt izmantota būvmateriālos kā saistviela, kā arī laku, krāsu un pārklājumu sastāvdaļa; -Kūdras granulas, var tikt izmantotas kā beramā siltumizolācija (siltumvadītspējas koef. 0.07 W/(mK)) un vieglo betonu ražošanā; -Kūdras-kokskaidu siltumizolācijas plātnes (siltumvadītspējas koef. 0.05 W/(mK)); -Kūdras-kokskaidu kompozītmateriāls ar stiprību spiedē līdz 1.75 MPa pie 10% deformācijām, kas var tikt izmantots ka konstruktīvai materiāls. Darba gaitā iegūtie materiāli ir ekoloģiski tīri un pilnība pārstrādājami, kas atbilst ekoloģiskās būvniecības pamatprincipiem. Visas izmantotās izejvielas ir vietējas un plaši izplatītas, kas materiāla ražošanas gadījumā sekmēs valsts ekonomikas attīstību.

Improving Quality of High Performance Concrete by Cavitation Treatment of the Raw Materials

The packing of fine aggregate affects the properties of HPC. The denser is fine aggregate packing the better are the workability, compressive strength and watertightness, and with that the frost and chemical resistances under sufficient paste content. Supplementary cementing materials such as silica fume has predominantly used for HPC due to it improves the packing of the concrete mix and activates the pozzolanic reaction. But agglomerates can be formed in this fine aggregate mix and therefore the packing of the mix is not improved, chemical reaction is hindered and the use of this aggregate may worsen the concrete properties instead of improving them. The effect of cavitation treatment on silica fume and cement is investigated in this work. Due to cavitation treatment, the agglomerate of silica fume and cement collapses into nano- and micro-particles and uniforms dispersion of small dispersed particles in liquid medium. Granulometric composition of silica fume slurry before and after cavitation treatment was determined. High performance concrete mixes with designed packing including micro- and nano-size fillers were elaborated. Fresh and hardened concrete were tested and such properties as cone flow, watertightness, water absorption and compressive strength were defined for control and experimental mixes. The influence of cavitation treatment of small dispersed raw materials on the compressive strength properties of produced concrete has been evaluated.

Cold-bonded biochar-rich lightweight aggregates for net-zero concrete

An emerging strategy to remove CO2 from the atmosphere and compensate for the greenhouse-gas emissions of cement and concrete is based on incorporating biochar into concrete. With this approach, concrete can be turned into a functional carbon sink (C-sink). Until now, biochar has been used without modification to replace part of the cement or of the aggregates in concrete. However, this technology comes with a number of practical problems, which include the high water absorption of the biochar (due to its high specific surface) and hazards (dust, risk of combustion). In this paper we present an alternative approach in which biochar is first processed into lightweight aggregates in a cold-bonding process. To this end, biochar is pelletized together with a small amount of hydraulic binder and with water and forms round pellets that further harden with hydration time. In this way, carbon-rich lightweight aggregates (C-LWA) are obtained that are easier to handle than the pure biochar. The C-LWA pellets have similar porosity and strength as conventional LWA and can be used for similar applications. Yet, the CO2 emissions from sintering traditional LWA are avoided and the C-LWA are instead an effective C-sink. We demonstrate that it is possible to incorporate in the pellets and eventually in the concrete a sufficient amount of carbon to compensate for the original emissions of concrete. The net-zero emissions concrete obtained with this approach possesses mechanical performance sufficient for typical structural applications in buildings

Improving Quality of High Performance Concrete by Cavitation Treatment of the Raw Materials

The packing of fine aggregate affects the properties of HPC. The denser is fine aggregate packing the better are the workability, compressive strength and watertightness, and with that the frost and chemical resistances under sufficient paste content. Supplementary cementing materials such as silica fume has predominantly used for HPC due to it improves the packing of the concrete mix and activates the pozzolanic reaction. But agglomerates can be formed in this fine aggregate mix and therefore the packing of the mix is not improved, chemical reaction is hindered and the use of this aggregate may worsen the concrete properties instead of improving them. The effect of cavitation treatment on silica fume and cement is investigated in this work. Due to cavitation treatment, the agglomerate of silica fume and cement collapses into nano- and micro-particles and uniforms dispersion of small dispersed particles in liquid medium. Granulometric composition of silica fume slurry before and after cavitation treatment was determined. High performance concrete mixes with designed packing including micro- and nano-size fillers were elaborated. Fresh and hardened concrete were tested and such properties as cone flow, watertightness, water absorption and compressive strength were defined for control and experimental mixes. The influence of cavitation treatment of small dispersed raw materials on the compressive strength properties of produced concrete has been evaluated

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

Cold-bonded biochar-rich lightweight aggregates for net-zero concrete

An emerging strategy to remove CO₂ from the atmosphere and compensate for the greenhouse-gas emissions of cement and concrete is based on incorporating biochar into concrete. With this approach, concrete can be turned into a functional carbon sink (C-sink). Until now, biochar has been mainly used without modification to replace part of the cement or of the aggregates in concrete. However, this technology comes with a number of practical problems, which include the high water absorption of the biochar (due to its high specific surface) and hazards (dust, risk of combustion). In this paper we present an alternative approach, in which biochar is first processed into lightweight aggregates in a cold-bonding process. To this end, biochar is pelletized together with water and a small amount of hydraulic binder forming round pellets that further harden with hydration. In this way, carbon-rich lightweight aggregates (C-LWA) are obtained that are easier to handle than the original biochar. The C-LWA pellets have similar porosity and strength as conventional LWA and can be used for similar applications. Yet, the CO₂ emissions from sintering traditional LWA are avoided and the C-LWA are instead an effective C-sink. We demonstrate that it is possible to incorporate in the pellets and eventually in the concrete a sufficient amount of carbon to compensate for the original emissions of concrete. The net-zero emissions concrete obtained with this approach possesses mechanical performance sufficient for typical structural applications in buildings.ISSN:0959-652