Advancing the use of secondary inputs in geopolymer binders for sustainable cementitious composites: A review

Because of concerns over the construction industry's heavy use of cement and the general dissatisfaction with the performance of building envelopes with respect to durability, there is a growing demand for a novel class of "green" binders. Geopolymer binders have re-emerged as binders that can be used as a replacement for Portland cement given their numerous advantages over the latter including lower carbon dioxide emissions, greater chemical and thermal resistance, combined with enhanced mechanical properties at both normal and extreme exposure conditions. The paper focuses on the use of geopolymer binders in building applications. It discusses the various options for starting materials and describes key engineering properties associated with geopolymer compositions that are ideal for structural applications. Specific properties, such as compressive strength, density, pore size distribution, cumulative water absorption, and acid resistance, are comparable to the specifications for structures incorporating conventional binders. This paper presents geopolymer binders, with their three dimensional microstructure, as material for structural elements that can be used to advance the realization of sustainable building systems. © 2011 by the authors

Mullitization behaviour during thermal treatment of three kaolinitic clays from Cameroon: Densificaron, sintering kinetics and microstructure

Three kaolinitic clays from Cameroon were studied for their mullitization behaviour. The three clayey materials were from Ntamuka (TAN), Mayouom (MAY) and Wabane (WAB), all situated in the hills of western Cameroon. X-ray diffraction and thermal, dilatometric and SEM-EDS analyses were used to follow up the phase evolution, sintering kinetics and microstructure of the three materials as a function of temperature (1000-1500°C). Fine powders of each sample were pressed and treated in the above temperature range with the goal to correlate the phase evolution with densificaron parameters (shrinkage, porosity, density and mechanical strength). The nucleation of mullite and the increase of peak intensities were directly correlated to continuous densification and reduction of open porosity as observed under the SEM, The mullitization peak temperatures at 5°C/min were 973°C, 979.1°C, and 983.6°C respectively for TAN, MAY and WAB and - in the same order but at 20°C/min 992.1°C, 997.4°C and 1001.2°C. The mullitization phenomenon, which includes a first step of nucleation and a second of crystal growth, shows an activation energy that varies depending on the nature of sample investigated: the values ranged from 650 to 730 kJ/mol. The microstructure of the sintered products consisted on the elongated secondary mullite (types II and III) interlocking with primary (type I) mullite in a compact matrix with relative amount of glassy phase for MAY and WAB. The morphology of mullite grains in TAN was more different being laiger cuboid grains aggregated with cristobalite to form a compact microstructure. The formation of TiO2 crystals and then Ti-Al (tialite: Al2TiO5) crystals influenced the microstructure of MAY and WAB

Superconducting and normal-state interlayer-exchange-coupling in La0.67_{0.67}Sr0.33_{0.33}MnO3{3}-YBa2_{2}Cu3_{3}O7−La_{7}-La_{0.67}SrSr_{0.33}MnO MnO{3}$ epitaxial trilayers

The issue of interlayer exchange coupling in magnetic multilayers with superconducting (SC) spacer is addressed in La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) - YBa$_{2}$Cu$_{3}$O$_{7}$ (YBCO) - La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ (LSMO) epitaxial trilayers through resistivity, ac-susceptibility and magnetization measurements. The ferromagnetic (FM) LSMO layers possessing in-plane magnetization suppress the critical temperature (T$_{c})$ of the c-axis oriented YBCO thin film spacer. The superconducting order, however, survives even in very thin layers (thickness d$_{Y} \sim$ 50 {\AA}, $\sim$ 4 unit cells) at T $<$ 25 K. A predominantly antiferromagnetic (AF) exchange coupling between the moments of the LSMO layers at fields $<$ 200 Oe is seen in the normal as well as the superconducting states of the YBCO spacer. The exchange energy J$_{1}$ ($\sim$ 0.08 erg/cm$^{2}$ at 150 K for d$_{Y}$ = 75 {\AA}) grows on cooling down to T$_{c}$, followed by truncation of this growth on entering the superconducting state. The coupling energy J$_{1}$ at a fixed temperature drops exponentially with the thickness of the YBCO layer. The temperature and d$_{Y}$ dependencies of this primarily non-oscillatory J$_{1}$ are consistent with the coupling theories for systems in which transport is controlled by tunneling. The truncation of the monotonic T dependence of J$_{1}$ below T$_{c}$ suggests inhibition of single electron tunneling across the CuO$_{2}$ planes as the in-plane gap parameter acquires a non-zero value.Comment: Accepted for publication in Phys. Rev.

Comportamento de cultivares de morango em cultivo orgânico na região sul do Estado de Sergipe.

O presente trabalho teve como objetivo verificar o comportamento das cultivares de morango nas condições edafoclimáticas de Umbaúba, SE, visando à recomendação de cultivares para cultivo orgânico em Sergipe. O experimento foi conduzido no campo experimental da Embrapa Tabuleiros Costeiros localizado no Município de Umbaúba, SE no período de 27 de junho a 09 de dezembro de 2013. Foram avaliadas oito cultivares (Ara, Aromas, Camarosa, Camino Real, Monterrey, Nina, Portola e San Andréas), em delineamento experimental de blocos casualizados com oito tratamentos, quatro repetições e parcela com 30 plantas no espaçamento de 35 cm x 35 cm. Na adubação utilizou como fontes de nutrientes a torta de mamona, hiperfosfato de gafsa, sulfato de potássio, bórax, sulfato de zinco e húmus de minhoca. Irrigação por gotejamento, ?mulching? nos canteiros com plástico preto dupla face, retiradas de folhas secas e doentes e dos estolões semanalmente. Para controle de pragas e doenças foram utilizados Fortneen para o controle de pulgão, calda sulfocálcica a 1% para controle do ácaro e calda viçosa para controle de doença

Genetic parameters for test day milk yields of first lactation Holstein cows by random regression models.

Covariance components for test day milk yield using 263 390 first lactation records of 32 448 Holstein cows were estimated using random regression animal models by restricted maximum likelihood. Three functions were used to adjust the lactation curve: the five-parameter logarithmic Ali and Schaeffer function (AS), the three-parameter exponential Wilmink function in its standard form (W) and in a modified form (W*), by reducing the range of covariate, and the combination of Legendre polynomial and W (LEG+W). Heterogeneous residual variance (RV) for different classes (4 and 29) of days in milk was considered in adjusting the functions. Estimates of RV were quite similar, rating from 4.15 to 5.29 kg2. Heritability estimates for AS (0.29 to 0.42), LEG+W (0.28 to 0.42) and W* (0.33 to 0.40) were similar, but heritability estimates used W (0.25 to 0.65) were highest than those estimated by the other functions, particularly at the end of lactation. Genetic correlations between milk yield on consecutive test days were close to unity, but decreased as the interval between test days increased. The AS function with homogeneous RV model had the best fit among those evaluated

Estimativas de parâmetros genéticos para a produção de leite em bovinos de corte.

Scanea

Investigation of volcanic ash based geopolymers as potential building materials

Volcanic ash powders from Etna (Italy) and Cameroon were used as the principal source of aluminosilicate to produce geopolymers with the potential for making building products. The volcanic ash was ball milled and reacted with concentrated alkaline solutions for polymerisation and subsequent curing at 75-400 °C for 12-48 h. It was found that the gel was more viscous than a similar gel formed from metakaolin. Geopolymers made from both ashes had bulk densities of 1.7-2.0 g/cm3 and water absorption values of 20-25 %. Their compressive strength values were 25-35 MPa and the bi-axial four-point flexura! strength values ranged from 14-20 MPa. These values increased by 20 % when cured for 21 d after 90 d storage. It was also found that by curing at 200-400 °C the mechanical properties increased. Scanning electron micrographs showed that with thermal curing microcrystalline phases were present along with undissolved crystalline phases. These phases remained bound to the matrix and acted as a filler for strengthening the materials. The Ca, Mg and Fe present as impurities in the volcanic ash formed some of these crystalline phases and did not form any deleterious hydroxide or carbonate phases

Characterization, reactivity and rheological behaviour of metakaolin and Meta-halloysite based geopolymer binders

The type of aluminosilicate precursor used in the synthesis of geopolymer binders plays a huge role in the resulting performance. Thus, it is critical to understand the properties of precursors and how they influence the corresponding performance of geopolymer binders. In this study, metakaolin and meta halloysite are used as the aluminosilicate precursor in the synthesis of geopolymer binders. These precursors are obtained locally in order to propel the sustainable development and application of geopolymers. The precursors were characterized and the corresponding influence on the reactivity, rheology and setting times of geopolymers was investigated. In addition to the influence of precursor type on the properties of the geopolymers, the effect of two silica moduli (i.e. 1.3 and 1.5) was also evaluated. The results from this study indicated that increasing the activator silica modulus from 1.3 to 1.5 extended the setting times and increased the stress strain of the geopolymer binders. Characterization of the precursors indicated that metakaolin has a higher amorphous content compared to that of meta halloysite. However, the finer particles of meta halloysite embodied it with the ability to participate in a faster geopolymerization and result in more formation of activation products