Effect of Pozzolanic Additives on the Strength Development of High Performance Concrete

The aim of this research is to estimate the effect of pozzolanic substitutes on the temperature generated by the hydration and on the final strength of concrete. Differential thermal analyses (DTA) were conducted. Ternary cementitious systems with different ratios of Portland cement, silica fume and calcined illite clay were investigated. The results showed that the rates of pozzolanic reaction and portlandite consumption in the silica fume-blended cement pastes are higher than in the illite clay-blended cement pastes.12th international conference “Modern Building Materials, Structures and Techniques” (MBMST 2016)The research leading to these results has received the funding from Latvia state research program under grant agreement "Innovative materials and smart technologies for environmental safety, IMATEH”

Study of the Course of Cement Hydration in the Presence of Waste Metal Particles and Pozzolanic Additives

As the construction of hydrotechnical and energy facilities grows worldwide, so does the need for special heavyweight concrete. This study presents the analysis of the influence of waste-metal particle filler (WMP) on Portland cement (PC) paste and mortars with pozzolanic (microsilica and metakaolin) additives in terms of the hydration process, structure development, and physical–mechanical properties during 28 days of hardening. Results have shown that waste-metal particle fillers prolong the course of PC hydration. The addition of pozzolanic additives by 37% increased the total heat value and the ultrasound propagation velocity (UPV) in WMP-containing paste by 16%; however, in the paste with only WMP, the UPV is 4% lower than in the WMP-free paste. The density of waste-metal particle fillers in the free mortar was about two times lower than waste-metal particle fillers containing mortar. Due to the lower water absorption, the compressive strength of WMP-free mortar after 28 days of hardening achieved 42.1 MPa, which is about 14% higher than in mortar with waste-metal particle filler. The addition of pozzolanic additives decreased water absorption and increased the compressive strength of waste-metal particle filler containing mortar by 22%, compared to pozzolanic additive-free waste-metal particle fillers containing mortar. The pozzolanic additives facilitated a less porous matrix and improved the contact zone between the cement matrix and waste-metal particle fillers. The results of the study showed that pozzolanic additives can solve difficulties in local waste-metal particle fillers application in heavyweight concrete. The successful development of heavyweight concrete with waste-metal particle fillers and pozzolanic additives can significantly expand the possibility of creating special concrete using different local waste. The heavyweight concrete developed by using waste-metal particle fillers is suitable for being used in load balancing and in hydrotechnical foundations

Use of Magnesium Silicate Contaminated with Organic Compounds in Ceramic Materials as a Pore Modifier

This study investigated the use of organic compound waste (OCW) contaminated magnesium silicate/diatomite in ceramics. Substituting part of the clay (between 5 and 20 wt.%) with OCW modifies a pore structure and enhances the ceramic product’s thermal conductivity, density, and frost resistance. Prepared samples were tested at 1000–1060 °C temperatures and their structural parameters and Maage factor, useful for frost resistance prediction, were evaluated. Results show that OCW modifies the porous structure and improves the insulating properties of the ceramic body. Increasing OCW content up to 15% in the ceramic body decreases density by up to 15.0%, and thermal conductivity by up to 42.5%, because of the modified pore structure. According to structural parameters calculation, the higher frost resistance can be predicted for ceramic bodies containing 5–10% of OCW, according to Maage factor calculation ceramic bodies containing 5–20% of OCW are frost resistant. Designed ceramic products can be attractive for use in construction due to improved energy efficiency and reduced energy consumption in buildings due to their low thermal conductivity, satisfactory mechanical strength, and sustainability based on predicted frost resistance

Effect of Calcium Nitrate on the Properties of Portland– Limestone Cement‐Based Concrete Cured at Low Temperature

The effect of calcium nitrate (CN) dosages from 0 to 3% (of cement mass) on the properties of fresh cement paste rheology and hardening processes and on the strength of hardened concrete with two types of limestone-blended composite cements (CEM II A-LL 42.5 R and 42.5 N) at different initial (two-day) curing temperatures (−10 °C to +20 °C) is presented. The rheology results showed that a CN dosage up to 1.5% works as a plasticizing admixture, while higher amounts demonstrate the effect of increasing viscosity. At higher CN content, the viscosity growth in normal early strength (N type) cement pastes is much slower than in high early strength (R type) cement pastes. For both cement-type pastes, shortening the initial and final setting times is more effective when using 3% at +5 °C and 0 °C. At these temperatures, the use of 3% CN reduces the initial setting time for high early strength paste by 7.4 and 5.4 times and for normal early strength cement paste by 3.5 and 3.4 times when compared to a CN-free cement paste. The most efficient use of CN is achieved at −5 °C for compressive strength enlargement; a 1% CN dosage ensures the compressive strength of samples at a −5 °C initial curing temperature, with high early strength cement exceeding 3.5 MPa but being less than the required 3.5 MPa in samples with normal early strength cementpublishedVersio

Investigations of low-cement castables with shamotte aggregate/Mažacemenčio kaitrai atsparaus betono su šamoto užpildu tyrimai

The castables with low-cement and normal quantity cement in its composition physical and mechanical properties was investigated. Aggregates of recycled shamotte waste, which are characterised by high water absorption, were used for castables. The results of influence of firing temperature on density and cold crushing strength for three series castables were determined (Fig 1 and 2). Thermal shock resistance, bending strength and deformations of the castables were investigated additionally (Table 2 and Fig 4). The results of investigations showed the advantage of low-cement castables: better thermal shock resistance, higher cold crushing and bending strength after firing at high temperature. The properties of developed low-cement and traditional castables produced with schamotte waste aggregates were compared with the data from German, Danish and Polish castables, a special quality shamotte aggregate was used (Table 1). Low-cement castable based on shamotte waste aggregates were developed and used for producing “Ipsen” furnace lining items. First Published Online: 26 Jul 201

Some aspects of influence of microsilica and admixtures on hydration kinetics of the alumina cement "Gorkal-40"

Theeffect of microsilica (in the amount from 7 to 35 % by the mass) and deflocculation admixture on setting and flowability of pastes with the cement "Gorkal-40", when W/C + S =0,3 is constant, was investigated. When the amount of microsilica is increased (from 7 to 35%) the flowability of the paste is decreased, while the addition of deflocculation admixture results in the increased flowability. The setting time is the lowest when the amount of microsilica in the paste is the highest. For the continuous registration of kinetics of hydration process of cement "Gorkal-40" the EXO (exothermic) method was used. The influence of microsilica and deflocculation admixture on the initial EXO effect as well as on the duration of the induction period and the main EXO effect was also established

The Effect of Natural and Synthesised Zeolites on Cement-Based Materials Hydration and Hardened State Properties

The synthesis of zeolites from difficult-to-utilise waste materials facilitates the creation of more financially attractive and efficient synthetic zeolites. These can be incorporated into construction materials, resulting in a reduction in cement usage and the production of superior, clean, and sustainable construction materials. The potential to enhance the hydration rate of fresh cement paste by substituting up to 10% of the cement with two synthetic zeolites—one commercially produced and the other synthesised from waste and natural zeolite—was explored. Due to a higher Al/Na ratio, newly sintered waste-based zeolite possesses six times higher electrical conductivity compared to industrially produced 4A zeolite and more than 20 times higher electrical conductivity compared to natural zeolite. As the sequence of this fact, substituting up to 10% of the cement with AX zeolite cement paste accelerates the maximum heat release rate time and increases the total heat by 8.5% after 48 h of hydration. The structure, compressive strength, and water absorption of the hardened cement paste depends on the Al/Na ratio, pH, and electrical conductivity values of the zeolite used. The findings revealed that AX zeolite, due to presence of mineral gibbsite, which speeds up hydration products, such as CSH development, increases the compressive strength up to 28.6% after 28 days of curing and reduces the water absorption by up to 1.5%. Newly synthesised waste-based AX zeolite is cheap because its production is based on waste materials and is mostly promising due to superior properties of created construction materials compared to the other presented zeolites

Effect of limestone particles on rheological properties and hardening process of plasticized cement pastes

The rheological properties (flow, fluidity, dynamic viscosity, stiffness rate) and hardening process (hydration, development of structure) of Portland - limestone cement (PLC) and Portland cement (PC) (strength class 42.5 R and N) pastes without and with superplasticizer (SP) based on synthetic polycarboxylatether (PCE) were investigated. It was found that limestone particles increase W/C and viscosity of cement pastes and reduction of water in plasticized pastes PCL is lower than in pastes PC. On the other hand, the fluidity of plasti cized cement pastes PCL is better and its thickening goes slower. The hydration and structure development in pastes PLC are going slower than in pastes PC. The impact of SP (when consistency of cement pastes is the same) on hydration process and hardening structure development of are going faster in plasticized cement pastes. The fineness of cements also has an influence on SP effect

Portlandcemenčių su aktyviais atliekiniais priedais kietėjimo proceso ypatumų tyrimai

<p>Darbe tiriamas naftos krekingo katalizatoriaus atliekų (FCC) ir žemakrosnės dulkių (CD) poveikis skirtingų CEM portlandcemenčių kietėjimo procesui ir fizikinėms mechaninėms savybėms. Tyrimams naudoti šie portlandcemenčiai pagal EN 197-1: CEM I 42,5 R (PCR), CEM I 42,5 N (PCN), CEM II/A-S 42,5 N (PCSN). Taikant ultragarso impulso sklidimo greičio (UIG) matavimo metodą, buvo tiriamas grynų portlandcemenčių (PC) tešlų ir tešlų, kuriose 10 % cemento buvo pakeista atliekiniais priedais, tarp jų ir gerai žinomu pucolaniniu priedu - silicio dioksido mikrodulkėmis (MS) - struktūros kitimas, taip pat mineralinės sudėties bei fizinių mechaninių savybių pokyčiai. Nustatyta, kad priedų poveikis priklauso tiek nuo paties priedo savybių (smulkumo, cheminės sudėties), tiek nuo cemento smulkumo bei mineralinės sudėties. CD iš tirtų priedų labiausiai mažina cemento tešlų išsiliejimo rodiklį. FCC poveikis kietėjančių cemento tešlų struktūros kitimui yra panašus kaip MS, tik ne toks ryškus. FCC pastebimai spartina tik smulkesnio cemento (PCR) pradinės struktūros susidarymą, kitiems cementams įtaka nedidelė. Toliau (po 24 h) visų cemento tešlų su FCC struktūra kurį laiką kinta lėčiau, tačiau po 28 parų jų struktūra jau tankesnė nei grynų cemento tešlų. Atitinkamai kinta ir stiprumo savybės: tešlų su FFC ankstyvasis stipris (po 2 parų) yra mažesnis, po 28 ir 90 parų - didesnis nei grynų cemento tešlų. CD poveikis tiek struktūros kitimui, tiek stiprio savybėms yra kitoks: pradžioje (iki 24 h) PCR ir ypač PCSN struktūra keičiasi sparčiau, PCN - beveik nekinta. Tolesnį kietėjančių tešlų struktūros tankėjimą CD priedas lėtina. Cementų ankstyvajam stipriui CD įtaka nedidelė, o po 28 ir 90 parų PCR ir PCN tešlų su CD priedu stipris mažesnis, PCSN - didesnis nei kontrolinių tešlų. Tokį poveikį tikriausiai nulėmė CD esančios šarminių elementų priemaišos (K⁺ ir Na⁺ katijonai). Šios priemaišos portlandcemenčių ankstyvąjį stiprį paprastai didina, o tolesnį jo augimą lėtina. PCSN struktūros stiprumas padidėja tikriausiai dėl šarminių priemaišų aktyvinamojo poveikio šlakams. OH^- jonų koncentracijos cemento suspensijose tyrimai parodė, kad pradžioje (iki 3 h) CD, panašiai kaip MS ir FCC, sumažina OH^- koncentraciją, tačiau toliau 28 paras ji didėja ir tampa gerokai didesnė nei kontrolinėse suspensijose.</p><p><a href="http://dx.doi.org/10.5755/j01.ms.17.1.254">http://dx.doi.org/10.5755/j01.ms.17.1.254</a></p

The Effect of Mechanical Activation of Fly Ash on Cement-Based Materials Hydration and Hardened State Properties

Fly ash from coal represents the foremost waste product of fossil fuel combustion. These waste materials are most widely utilised in the cement and concrete industries, but the extent of their use is insufficient. This study investigated the physical, mineralogical, and morphological characteristics of non-treated and mechanically activated fly ash. The possibility of enhancing the hydration rate of the fresh cement paste by replacing part of the cement with non-treated and mechanically activated fly ash, and the hardened cement paste’s structure and early compressive strength performance, were evaluated. At the first stage of the study, up to 20% mass of cement was replaced by untreated and mechanically activated fly ash to understand the impact of the mechanical activation on the hydration course; rheological properties, such as spread and setting time; hydration products; mechanical properties; and microstructure of fresh and hardened cement paste. The results show that a higher amount of untreated fly ash significantly prolongs the cement hydration process, decreases hydration temperature, deteriorates the structure and decreases compressive strength. Mechanical activation caused the breakdown of large porous aggregates in fly ash, enhancing the physical properties and reactivity of fly ash particles. Due to increased fineness and pozzolanic activity by up to 15%, mechanically activated fly ash shortens the time of maximum exothermic temperature and increases this temperature by up to 16%. Due to nanosized particles and higher pozzolanic activity, mechanically activated fly ash facilitates a denser structure, improves the contact zone between the cement matrix, and increases compressive strength up to 30%