[Show abstract][Hide abstract] ABSTRACT: The effect of nano-size particles of amorphous silica (nanosilica) on the rheological behaviour and mechanical strength development of cementitious mixes is addressed. Mini-slump and rheometric tests were carried out on cement pastes made with three dose levels of nanosilica at different water/binder ratios. Cement paste workability resulted to be significantly lower than expected for the adopted water/binder ratios, as a consequence of instantaneous interactions between nanosilica sol and the liquid phase of cement pastes, which evidenced the formation of gels characterised by a significant water retention capacity. The resulting reduction of the mix workability was avoided by suitable addition procedures of superplasticizers. No appreciable improvement in the compressive strength development of cementitious mixes by nanosilica addition was observed, in contrast with some results from literature. This confirms conflicting experience on the problem, but some parameters affecting the strength development were identified and discussed.
Construction and Building Materials 10/2012; 35:666–675. · 2.29 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A new leaching test on comminuted (0.125-2.0mm gradation) cementitious matrices, designated as Modified-Pore Water (M-PW) test, was developed to evaluate the effect of varying leachate pH (4-12.8) and/or liquid-to-solid, L/S, ratio (0.6-50 dm(3)/kg) on the availability factor, F(AV), of heavy metals. The M-PW test was applied to leaching of lead and zinc ions from ground Portland cement mortar incorporating Municipal Solid Waste Incinerator (MSWI) fly ash. Correlation of M-PW test results (F(AV)-L/S data) allowed the determination of the pore-liquid availability factor, F(AVP), at different leachate pHs. These F(AVP) values were utilized, in conjunction with a kinetic pseudo-diffusional model, to evaluate the leaching behavior of monolithic mortar specimens subjected to dynamic leaching tests (constant leachant pH 4 or 6).A good agreement was found between the effective diffusion coefficients, D(e), of lead and zinc ions calculated by such a methodological approach and those obtained from recognized microstructural models. In contrast, no satisfactory agreement was found when these D(e) values were compared with the ones calculated from the results of other availability tests on granular solid samples (NEN 7341 and AAT tests).
Journal of hazardous materials 04/2012; 227-228:1-8. · 4.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The feasibility of using woody biomass fly ash (WBFA) as a mineral admixture in cement-based materials was investigated. This
fly ash was characterized for chemical composition and used to prepare a cement blend with 70wt% Portland cement and 30wt%
WBFA. Cubic specimens were cast from a blended cement paste (water-to-binder ratio 0.50) and, after 28 days of curing at 20°C
and 100% relative humidity, these specimens were tested for heavy metal leachability through the use of a sequential leaching
protocol, at a constant pH of leachant (deionized water; pH6.0). It was found that, except for the chloride content, the
WBFA is able to meet the European chemical requirements established for reuse of coal fly ash in cement-based materials. Although
the WBFA is characterized by a significant content of heavy metals of particular environmental concern (Cd, Cr, Cu, Ni, Pb,
Zn), the results of the monolith leaching test have shown a good immobilization capacity of such metals by the cementitious
matrix and, consequently, a good environmental quality of the blended cement investigated.
[Show abstract][Hide abstract] ABSTRACT: The primary objective of this study was to ascertain whether the Threshold Alkali Level (TAL) of the concrete aggregates may be taken as a suitable reactivity parameter for the selection of aggregates susceptible of alkali-silica reaction (ASR), even when ASR expansion in concrete develops under restrained conditions. Concrete mixes made with different alkali contents and two natural siliceous aggregates with very different TALs were tested for their expansivity at 38°C and 100% RH under unrestrained and restrained conditions. Four compressive stress levels over the range from 0.17 to 3.50N/mm2 were applied by using a new appositely designed experimental equipment. The lowest stress (0.17N/mm2) was selected in order to estimate the expansive pressure developed by the ASR gel under “free” expansion conditions. It was found that, even under restrained conditions, the threshold alkali level proves to be a suitable reactivity parameter for designing concrete mixes that are not susceptible of deleterious ASR expansion. An empirical relationship between expansive pressure, concrete alkali content and aggregate TAL was developed in view of its possible use for ASR diagnosis and/or safety evaluation of concrete structures.
Cement and Concrete Research - CEM CONCR RES. 01/2010; 40(9):1403-1409.
[Show abstract][Hide abstract] ABSTRACT: The reuse of cement-solidified Municipal Solid Waste Incinerator (MSWI) fly ash (solidified/stabilised (S/S) product) as an artificial aggregate in Portland cement mortars was investigated. The S/S product consisted of a mixture of 48 wt.% washed MSWI fly ash, 20 wt.% Portland cement and 32 wt.% water, aged for 365 days at 20 degrees C and 100% RH. Cement mortars (water/cement weight ratio=0.62) were made with Portland cement, S/S product and natural sand at three replacement levels of sand with S/S product (0%, 10% and 50% by mass). After 28 days of curing at 20 degrees C and 100% RH, the mortar specimens were characterised for their physico-mechanical (porosity, compressive strength) and leaching behaviour. No retardation in strength development, relatively high compressive strengths (up to 36 N/mm2) and low leaching rates of heavy metals (Cr, Cu, Pb and Zn) were always recorded. The leaching data from sequential leach tests on monolithic specimens were successfully elaborated with a pseudo-diffusional model including a chemical retardation factor related to the partial dissolution of contaminant.
Journal of Hazardous Materials 04/2008; 151(2-3):585-93. · 4.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A step-wise treatment of Municipal Solid Waste (MSW) incinerator fly ash including washing, milling and sintering was investigated in order to manufacture ceramic materials with improved physical, mechanical and environmental properties and, possibly, to reduce the power input of the sintering process. An interpretation of the test results based on the microstructure of sintered products and sintering kinetic modeling was also attempted to identify the densification mechanisms. It was found that milling of washed fly ash represents a basic step for manufacturing high-density ceramic materials with very high compressive strengths (up to 500 N/mm2). A significant reduction in the power input of the sintering process (reduction of firing temperature from 1210 degrees C for washed fly ash to 1140 degrees C for milled-washed fly ash) is also achieved. A dense, well-sintered microstructure is formed through an intermediate-stage, liquid-phase sintering mechanism controlled by liquid-phase diffusion and grain shape accommodation. Such a microstructure is able to strongly immobilise heavy metals, thus giving good environmental properties to sintered product.
[Show abstract][Hide abstract] ABSTRACT: In this study, the suitability of the threshold alkali level, TAL, the kinetic parameter, In k, and the microstructural disorder
coefficient, Cd, of the aggregates, taken as alkali-silica reactivity criteria, was assessed using different typologies of
Italian natural ASR-susceptible aggregates of known field performance. The TAL, In k, and Cd were determined using a modified
version of the RILEM AAR-3 concrete prism expansion test, the ASTM C1260 mortar-bar expansion test, and the infrared spectroscopy
test, respectively. It was found that the three reactivity criteria are all appropriate for discriminating between reactive
and innocuous aggregates. However, the TAL proves to be a more suitable criterion for interpreting the field performance data
of the aggregates investigated. There exists a linear relationship between TAL and In k, or between TAL and Cd, which provides
a rapid means of estimating the threshold alkali levels of ASR-susceptible aggregates from the results of the ultra-accelerated
mortar-bar test and/or the infrared spectroscopy test. A TAL-based classification of the degree of reactivity of the aggregates,
as well as some modifications of the reactivity domains established by the infrared spectroscopy method are also proposed.
Dans cette étude on a vérifié la fiabilité du Niveau de Seuil des Alcalis, NSA, du paramètre cinétique, In k, et du coefficient
de désordre microstructurel, Cd, comme critères de réactivité alcalis-silice (A-S), en utilisant de différentes typologies
de granulats naturels d'origine italienne susceptibles de manifester cette réactivité et dont le comportement en service à
long terme était bien connu. Les paramètres de réactivité NSA, In k et Cd ont été déterminés respectivement au moyen de l'essai
d'expansion sur des éprouvettes de béton RILEM AAR-3 dûment modifié, de l'essai d'expansion sur des éprouvettes de mortier
ASTM C1260 et de l'essai de spectrographie infrarouge. Les résultats montrent que tous les trois critères sont bien appropriés
pour distinguer les granulats réactifs de ces non réactifs. Toutefois, le paramètre NSA se révèle le plus approprié pour évaluer
les donnés de comportement en service des granulats examinés. Il existe une relation linéaire entre NSA et In k, ou entre
NSA et Cd, en mesure de fournir un moyen rapide pour estimer le Niveau de Seuil des Alcalis des granulats susceptibles de
réaction A-S à partir des résultats de l'essai ultra-accéléré sur des éprouvettes de mortier et/ou de la spectrographie infrarouge.
On a aussi proposé un classement du niveau de réactivité des granulats basé sur le paramètre NSA et un changement des critères
de réactivité établis par la méthode de spectrographie infrarouge.
Materials and Structures 01/2005; 38(3):373-380. · 1.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Cette étude a eu pour but de vérifier la fibilité de la méthode de qualification française AFNOR P18-542  et de son équivalent
canadien CSA A23.2-27A , lorsque ces dernières sont utilisées pour évaluer la réactivité potentielle alcalis-silice (A-S)
de certains sables siliceux naturels d'origine italienne, dont le comportement en service à long terme était déjà bien connu.
On a également mis au point une nouvelle méthodologie de qualification qui repose sur l'utilisation de l'examen pétrographique
(ASTM C295) , de l'essai d'expansion sur mortier MICROBAR (AFNOR P18-588)  et d'une méthode de détermination du niveau
de seuil des alcalis, NSA . S'il a été démontré que la méthode de qualification canadienne n'est pas la plus indiquée pour
évaluer la réactivité potentielle A-S des sables examinés, l'évaluation diagnostique fournie par la méthodologie française
semble quant à elle pleinement satisfaisante. Toutefois, ces deux méthodes semblent inadéquates lorsqu'il s'agit de prévoir,
en termes rigoureux, le comportement expansif d'un granulat donné, en réponse à une variation de la composition et/ou des
conditions d'exposition ambiante du béton. Par contre, la méthodologie de qualification proposée, qui repose essentiellement
sur le niveau de seuil des alcalis, NSA, servant de paramètre de réactivité pour les granulats siliceux, semble présenter
de meilleures garanties, tout du moins en ce qui concerne les sables examinés.
In this study, the reliability of both the French (AFNOR P18-542)  and the Canadian (CSA A23.2-27A)  test methodologies
for the qualification of aggregates susceptible of alkali-silica (A-S) reaction in concrete was verified on some Italian natural
siliceous sands of known long-term field performance. A new test methodology, based on the utilization of the petrographic
examination (ASTM C295) , the mortar-microbar expansion test (AFNOR P18-588)  and a method of determination of the
threshold alkali level, TAL,  was also developed. It was found that the Canadian test methodology does not appear to be
appropriate for evaluating the potential alkalireactivity of the tested sands. Conversely, a correct diagnosis for the A-S
reactivity of these sands is obtained through the use of the French test methodology. However, both test methodologies do
not appear suitable for strictly predicting the expansive behaviour of a given aggregate when subjected to variations of composition
and/or environmental exposure conditions of concrete. The proposed test methodology, which is essentially based on the use
of the threshold alkali level, TAL, as a reactivity parameter, appears to be more appropriate for such a prediction, at least
for the sands investigated.
Materials and Structures 06/2003; 36(5):302-310. · 1.39 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The solidification/stabilization (S/S) process of municipal solid waste (MSW) fly ash in cementitious matrices was investigated in order to ascertain the feasibility of a washing pretreatment of fly ash with water as a means of maximizing the ash content of cementitious mixtures. Four types of fly ash resulting from different Italian MSW incineration plants and ASTM Type III Portland cement were used in this study. Ash-cement mixtures with different fly ash/cement (FA/C) ratios were made using untreated and washed fly ash. Washing of fly ash with water was realized by a two-stage treatment (liquid/solid=25; mixing time=15 min for each stage). The cementitious mixtures were characterized for water demand, setting time, mechanical strength, and heavy metals leachability. Comparison between the above properties of mixtures incorporating untreated and washed fly ash (particularly, setting characteristics), coupled with economical evaluation of the S/S process when applied to untreated and washed fly ash, proved the feasibility of washing pretreatment as a means of maximizing the incorporation of MSW fly ash in cementitious matrices (ash content up to 75%-90% by weight of total solid).
Journal of Hazardous Materials 12/1999; 70(1-2):53-70. · 4.33 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: A modified version of the ultra-accelerated concrete prism expansion test in alkaline solutions at 150°C (testing concrete mixes at varying alkali content of concrete) was investigated in order to ascertain the reliability of this test method for evaluating the threshold alkali levels (TAL) of alkali-reactive siliceous aggregates in concrete. Five natural sands of known field performance were tested and their TAL values determined by the ultra-accelerated test were compared with those obtained from concrete prism expansion tests at 38°C and 100% RH. A correlation between the threshold alkali level of the sands and their microstructural disorder coefficient, Cd, as measured by infrared spectroscopy, was also attempted. The modified ultra-accelerated concrete prism test proved to be a rapid and reliable method for evaluating the threshold alkali level of reactive siliceous aggregates in concrete, provided that an expansion limit of 0.11% at 3 weeks was taken as the reactivity judgement criterion for this test. The threshold alkali level proved to be an appropriate reactivity parameter for the selection of alkali-reactive siliceous aggregates. Also, the existence of a straight-line relationship between TAL and Cd suggested the possibility of developing a new test methodology for estimating TAL, based on Cd measurements by infrared spectroscopy.
Cement and Concrete Composites 01/1999; 21(4):325-333. · 2.76 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The use of the mortar bar expansion test in a 1 M NaOH solution at 80°C as a means of assessing the effectiveness of fly ash and silica fume against alkali-silica reaction was investigated using fused quartz as reactive aggregate. Long-term ASTM C227 test results were utilized for comparative purposes. The NaOH bath test provides reasonable results about the minimum contents of fly ash and silica fume needed to prevent deleterious expansion in mortars containing fused quartz. Particularly for silica fume, agreement between the minimum admixture contents predicted by the two test methods is found only when the expansion limits of 0·25% at 12 days and 0·10% at 1 year or, alternatively, 0·15% at 14 days and 0·05% at 1 year are used for the NaOH bath and ASTM C227 test methods, respectively. A consistent relationship exists between the expansion of mortar bars and the Na+ ion concentration in the pore solution after 14 days immersion of the specimens in the NaOH solution. With both test methods there is no direct correlation between the performance of fly ashes and their total and available alkali contents.
[Show abstract][Hide abstract] ABSTRACT: The ability of Fuller's earth to adsorb quaternary ammonium surfactants from aqueous solutions was studied as a function of the molecular weight of surfactant, the particle size of adsorbent and the solution pH. The adsorption of these compounds on Fuller's earth was found to be a relatively slow process, particularly when the particle size range of earth is 150 to 180 m. The adsorption isotherms were of the Langmuir-type. The equilibrium adsorption capacity increased as the molecular weight of surfactant was increased or a finer grain size fraction of earth was used. The change in the solution pH over the range of 7.0 to 9.0 did not affect the adsorption of surfactants studied on Fuller's earth.
Water Air and Soil Pollution 08/1990; 53(1):139-150. · 1.75 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The effect of the addition time of superplasticizers on the workability of concretes containing 0 or 10% microsilica was studied at different polymer dosages, water/cement ratios and mixing times. Cement pastes were also prepared and examined for workability, zeta potential and polymer adsorption. The water demand and the slump loss of the two types of concretes, as well as the dosage of superplasticizer, are significantly reduced when the addition of the polymer is delayed. Regardless of the addition time of the admixture, the difference in water demand between the two types of concretes is greatly reduced when the polymer dosage is above 2% by weight of cement. The data on cement pastes suggest that the delayed addition of superplasticizer might be assimilated to an immediate addition to a cement with a lower fireness.
Cement and Concrete Research - CEM CONCR RES. 01/1988; 18(3):351-362.
[Show abstract][Hide abstract] ABSTRACT: A methodological approach, based on some innovative reactivity parameters such as the threshold alkali level (TAL) of aggregates and the tolerable driving force (Δtol) of the deleterious expansive process associated with alkali–silica reaction (ASR), is proposed in order to assess the alkali-reactivity of aggregates and compare the effectiveness of different types of ASR inhibitors (low-alkali Portland cements, lithium compounds, and blended cements manufactured with active mineral additions). The effectiveness of the ASR inhibitors, expressed in terms of Δtol, is related to the naturally available alkali content of concrete and the TAL of the aggregate used in the concrete mix. The potential minimum contribution of alkalis (L
im) by a given ASR inhibitor to the concrete mix is proposed as a specific efficacy parameter. The relationships between the effective dose levels of mineral additions or lithium compounds and the efficacy parameters Δtol and L
im have also been identified. The test procedures for the experimental determination of such parameters are described and some methodology applications to published ASR expansion data are reported.
Materials and Structures 46(6). · 1.39 Impact Factor