Thermal analysis was first used to investigate the pattern of dissociation of hydrated ordinary Portland cement. Portlandite
(Ca(OH)2) decomposes at about 500C. This was confirmed by kinetic calculations. Thermal analysis was then performed to establish
the effect of varying the cement content on the percent mass loss associated with the decomposition of Ca(OH)2 in cement mortar cured for 28 days. An increasing relation was obtained. Standard concrete cubes were then prepared with
cement contents ranging from 200 to 450 kg m-3. The loss in mass on heating, up to 750C, of concrete samples cured for 28 days was then related to the cement content in
concrete. The relation obtained was tested for concrete cubes of known cement content and found to be in better agreement
than the results obtained by conventional chemical analysis. This method can be used for an approximate determination of the
cement content in concrete.
Authors:J. Lawry, A. Ray, D. Klimesch, P. Thomas, J.-P. Guerbois, and J. Harrison
Summary Due to growing environmental concerns and the need to use less energy-intensive building products, alternatives and improvements to Portland cement (PC) are being actively researched worldwide. Use of supplementary materials is now a common practice where PC is the predominant component of inorganic building products. This study aims to investigate the potential of magnesia (MgO), derived from a naturally occurring raw material magnesite, as a supplementary material. Results from mortar samples prepared with 10 and 20% replacements of ordinary Portland cement (OPC) by MgO are presented. DTA-TG was used to study and characterise the hydration behaviour of MgO in OPC environment after 3, 7, 14, 28, 56 and 90 days of moist curing. Microstructural and compressive strength determinations providing additional information on the influence of hydrated phases are also reported.
Authors:Marek Gawlicki, Wiesława Nocuń-Wczelik, and Łukasz Bąk
Calorimetry was applied to an investigation of the early hydration of Portland cement (PC)–calcium aluminate cement (CAC)
pastes. The heat evolution measurements were related to the strength tests on small cylindrical samples and standard mortar
bars. Different heat-evolution profiles were observed, depending on the calcium aluminate cement/Portland cement ratio. The
significant modification of Portland cement heat evolution profile within a few hours after mixing with water was observed
generally in pastes containing up to 25% CAC. On the other hand the CAC hydration acceleration effect was also obtained with
the 10% and 20% addition of Portland cement. As one could expect the compressive and flexural strength development was more
or less changed—reduced in the presence of larger amount of the second component in the mixture, presumably because of the
internal cracks generated by expansive calcium sulfoaluminate formation.
Authors:Ewa Stepkowska, M. Aviles, J. Blanes, and J. Perez-Rodriguez
The low temperature
of decomposition of some calcium carbonates and the bending of the TG curves
of hydrated cement between 500 and 800°C suggested the presence of some
complex compound(s), which needed complementary investigation (XRD, TG). Stepwise
transformation of portlandite (and/or lime) into calcium carbonate, with intermediate
steps of calcium carbonate hydroxide hydrates (CCH-1 to CCH-5), was indicated
by the previous study of two OPC.
This was checked here on four
cements ground for tg=15,
20, 25 and 30 min and hydrated either in water vapour, successively at RH=1.0,
0.95 and 0.5 for 2 weeks each (WR1, WR2 and WR3, respectively) or as mortars
in liquid water (1m), followed by WR as above. The d spacing of portlandite
was confirmed to vary: here between the lowest and the highest standard values.
The diffractograms of n=32 different samples
were analyzed for presence of standard CCH peaks, generally slightly displaced.
These were: CCH-1 [Ca3(CO3)2(OH)2]: N=11 peaks, of three different d[hkl] spacings, CCH-2 [Ca6(CO2.65)2(OH657)7(H2O)2]: N=10 for two d[hkl], CCH-3 [Ca3(CO3)2(OH)2·1.5H2O]: N=14 for five d[hkl], CCH-4,
ikaite [CaCO3(H2O)6]: N=13 for six d[hkl], CCH-5[CaCO3(H2O)]: N=15 for five d[hkl]. Thus the most probable is the presence of the
last three. The stepwise transformation of Ca(OH)2
into CaCO3 was confirmed:
portlandite (varying d)→CCH-1→CCH-2→CCH-3→CCH-4→CCH-5→CaCO3
The content of CCH was the highest at tgr=15
min, decreasing down to tgr=25
min and increasing slightly at 30 min, as inferred from the number of the
peaks observed. After cement powder hydration at RH=1.0 (WR1) peak number
increased gradually from CCH-1 to CCH-5, whereas in the hydrated mortar (1m)
the peak number decreased from CCH-1 to CCH-5, indicating the respective progress
of the carbonation reaction.
Vitreous solder glasses, such as Mansol #40 and FEG-2002, are commercialized solder glasses, which are compression sealing
glasses that can be used to solder materials with expansions between 55-68⊙10-7C-1, such as Al2O3.
In order to understand and tailor the thermal behaviour of solder glasses, cylindrical-like glasses were first carefully ground
with a stainless steel mortar and pestle. Initially, no exothermic or endothermic data were obtained from the DTA/DSC curves
except those relating to melting. However, exothermic peaks appeared after the glass samples were re-melted. In this work,
kinetic parameters such as the activation energy, and the morphology of the devitrification mechanisms for two kinds of solder
glasses were also investigated, using non-isothermal DTA techniques. The activation energies ranged from 220 to 235 kJ mol-1 and the devitrification mechanism parameters were close to 1. This indicates that the devitrification mechanisms of the two
kinds of solder glasses involve surface nuclei.
Montmorillonite (M) saturated with H+,Li+,Na+,K+,Rb+,Cs+,NH4+,Mg2+,Ca2+,Sr2+,Ba2+,Mn2+,Co2+,Cu2+,Al3+ and Fe3+ were dry-ground with urea (U) in mass ratios U/M between 0.1 and 2.0 in an agate mortar and diffracted by X-ray. Extensive swellings occurred with H-, Li-, Na-, di-and trivalent
cation-clays, suggesting the formation of urea-montmorillonite intercalation complexes. Mechanochemically treated samples
were heated at different temperatures up to 375°C. The rise in temperature was accompanied by a decrease in the basal spacing.
There was a correlation between the results of the thermo-XRD-analysis and the fine structures of the urea-montmorillonite
complexes described in the literature. Five stages in the basal spacing vs. temperature curves were identified. In the first stage (at 150°C) the decrease was due to dehydration. In the second stage
(175°C) this dehydration was accompanied by some thermal intercalation of excess urea. The other stages (at 225, 325 and 375°C)
were associated with the degradation of urea and the condensation of the degraded species to polymeric products. At 375°C
Li-, Na-, K-NH4-, Mh-, Co- and Cu-montmorillonite collapsed, indicating that urea was evolved. The other urea-clay complexes did not collapse
due to intercalated polymers formed by the degradation products of urea.
Authors:Alina Bădănoiu, Jenica Paceagiu, and Georgeta Voicu
The hydration and hardening processes of Portland cements prepared from clinkers mineralized with sodium fluoride and/or oxides (SnO2 or CuO) was studied. Type I cements (CEM I) were prepared by grinding with gypsum (5%) of clinkers obtained by the burning of an industrial raw mix with different mineralizers: sodium fluoride, oxides (CuO and SnO2) or mixtures of sodium fluoride and oxide (NaF + CuO or NaF + SnO2). The influence of foreign ions on the clinker morphology was assessed by scanning electronic microscopy (SEM) and energy dispersive X-ray spectrometry (EDX). The hydration processes of modified cements were examined by X-ray diffraction analysis (XRD) and thermal analysis techniques (TG and DTA). The main properties of the cements, i.e., flexural and compressive strengths, setting time, and soundness were also determined. A good correlation between the chemically bound water or portlandite content in pastes hydrated 2–28 days and compressive strength developed by mortars was observed. The influence of mineralizers on the kinetic of hydration processes and main properties of cements is different—0.5% NaF and 0.5% SnO2 and their mixture increase the rate of cement hydration and hardening processes, opposite to 0.5% CuO that reduce the rate.
A mai mérnöki gyakorlatban a falazatok alakváltozási jellemzőit kísérleteken alapuló, fenomenológiai összefüggések segítségével határozzák meg. A cikkben arra a kérdésre keressük a választ, hogy meg lehet-e határozni a falazatot alkotó összetevők – a falazóelem, illetve a habarcs – alakváltozási jellemzőinek, geometriájának és a kötési módnak az ismeretében a falazat rugalmassági és nyírási modulusát. A cikk röviden ismerteti az alakváltozási jellemzők meghatározásának elméleti módjait, és új homogenizációs modelleket mutat be kitöltetlen állóhézagú falazat alakváltozási jellemzőinek meghatározására.
A bemutatott és az általunk alkotott modellek használhatóságát végeselem-módszerrel igazoltuk.
Authors:Yong-Sam Chung, Jong-Hwa Moon, Sun-Ha Kim, Sang-Hoon Kang, and Young-Jin Kim
To enhance the applicability of the nuclear analytical technique in the field of industry and the environment, the inorganic
elemental content of the bottom ash from a municipal solid waste incinerator was determined by instrumental neutron activation
analysis. Bottom ash samples were monthly collected from an incinerator located at a metropolitan city in Korea, strained
through a 5 mm sieve, dried by an oven and pulverized by an agate mortar. The samples were irradiated at the NAA #1 irradiation
hole (thermal neutron flux: 2.92·1013 n·cm−2·s−1) in the HANARO research reactor of the Korea Atomic Energy Research Institute and the irradiated samples were measured by
a HP Ge gamma-ray spectrometer. Thirty-three elements including As, Cr, Cu, Fe, Mn, Sb and Zn were analyzed by an absolute
method. The quality control was conducted by a simultaneous analysis with NIST standard reference materials. The average concentrations
of the major elements such as Ca, Fe, Al, Na, Mg, K and Ti measured in the sample were 19.9%, 4.85%, 3.79%, 2.11%, 1.84%,
1.22% and 1.02%, respectively. In addition, the concentrations of the hazardous metals like Zn, Cu, Cr, Sb and As were 0.77%,
0.31%, 729 mg·kg−1, 116 mg·kg−1 and 22.2 mg·kg−1, respectively.