E. Peris-Mora

Mechanical treatment of fly ashes. Part I: Physico-chemical characterization of ground fly ashes

Physico-chemical characteristics of mechanically treated fly ashes are investigated. An original fly ash was ground, using a laboratory mill, for several times (from 10 to 60 minutes). Respect to physical characterization, fineness increasing of samples with grinding time was observed, but loss of effectiveness occurred for grinding time longer than 20 minutes. Ground samples showed higher specific gravity probably due to the presence of cenospheres in the original fly ash. Only a little change in mineralogical composition of fly ashes was observed when grinding: calcium carbonate formation by reaction of calcium oxide with carbon dioxide. Chemical behavior (pH and conductivity) of fly ash/water suspensions were studied and acid neutralization capacities measured.

Mechanical treatment of fly ashes part II: Particle morphologies in ground fly ashes (GFA) and workability of GFA-cement mortars

Abstract Mechanical treatment (by grinding) effects on particle morphology and specific gravity of fly ashes, and workability of ground fly ash (GFA) cement mortars have been studied. Different shape morphologies of GFA particles have been established: shell shaped and irregular solid fragments. Real and bulk specific gravity values were measured, proving that grinding process increased the content of poor shape particles. Particle Packing Factor (PPF) for GFA decreased below 50%. Workability of GFA-cement mortars is negatively affected, but it is still greater that only cement mortar one. Good correlations between flow table spread (FTS) values per water volume unit and fly ash replacing percentage have been obtained, and a relative workability factor W r is established. Determination of W r value permits to compare the effect of grinding or other fly ash processing methods on workability of mortars. Finally, good linear relationships between W r values and the inverse of mean diameter particle or calculated specific surface area were found.

Mechanical behavior of mortars containing sewage sludge ash (SSA) and Portland cements with different tricalcium aluminate content

The influence of sewage sludge ash (SSA) on cement mortars strength has been studied. To evaluate better the increase of strength compared to control mortar, relative compressive strength gain (CSGr) and flexural strength gain (FSGr) were calculated. The experience shows that SSA behaves as an active material, producing an increase of compressive strength compared to control mortar, probably due to pozzolanic properties of SSA. It can be emphasized that high sulfur content of SSA (12.4%) does not seem to have influence on compressive strength of mortars containing SSA. When CSGr of mortars containing different types of cements are compared, no clear correlation is observed between CSGr and C3A content in cement.

Early-strength development of portland cement mortars containing air classified fly ashes

Abstract A study of the effect of different fly ash sized fractions on compressive and flexural strength of blended cement mortar is presented. Mortars containing fly ashes, replacing 15 to 60 % of Portland cement, were prepared, and compressive and flexural strengths compared with “only cement” mortar. The influence of curing temperature was also studied. The study reveals that: a) compressive and flexural strength for mortars containing fly ash (or their sized fractions) are significantly enhanced when curing temperature is raised; b) the content of fly ash finest particles (less than 10 μm) is a crucial parameter for yielding a compressive strength enhancement; c) Good correlations between strengths and particle mean diameters were observed when fly ash percentage of substitution was 60 %.

A preliminary study of fly ash granulometric influence on mortar strength

Abstract The effect of replacing 30 % of portland cement by Spanish fly ash (class F according to ASTM C-618) and their sized fractions obtained using sieves on compressive and flexural strength of mortars was investigated. The study reveals an enhancement of compressive strength when fineness of fly ash fraction increases, particles with diameter less than 10 μm being crucial.

Comparisons among magnetic and non-magnetic fly ash fractions: Strength development of cement-fly ash mortars

Magnetic extractions from aqueous-fly ash suspensions produced magnetic and non-magnetic fly ash fractions. Several fractions were obtained from an original fly ash (T0), from T0 and further grinding, and from a ground fly ash (T60). Magnetic and non-magnetic samples were characterized: chemical composition, granulometric data, specific gravity and specific surface area. Workability studies on mortars containing these fractions were carried out. Generally, non-magnetic fractions yielded mortars with similar or higher flowability than mortars containing the corresponding magnetic fractions. On the other hand, compressive strength development studies showed that non-magnetic fractions are more pozzolanic than magnetic ones; moreover, optimum replacing percentage of cement by fly ash fractions was 45% for non-mechanically treated samples, whereas for ground fractions optimum values were 30% for non-magnetic samples and 45% for magnetic ones.

Studies on crystalline rice husk ashes and the activation of their pozzolanic properties

Characterization, pozzolanic activity determination and pozzolanic activation of rice husk ashes (RHA) containing a high percentage of crystalline silica have been carried out. Two RHA samples from incineration plant and another RHA sample from energy-recovery combustion plant have been compared. Several techniques such as X-ray diffractometry, solubility in boiling KOH solution, conductivity and thermogravimetric monitoring of RHA/lime systems and strength development of RHA/cement mortars have been used for evaluating pozzolanic activity or RHA. Additionally, mechanical treatment of RHA by grinding and increase of curing temperature of RHA containing mixtures became appropriate procedures for activating pozzolanic activity of highly crystalline RHA. The effectiveness of chemical activators such as NaOH solution and powdered Ca(OH)2 also was studied.

Study of cement-based mortars containing Spanish ground sewage sludge ash

A study of cement based mortars containing spanish ground sewage sludge ash is presented. The influence of original and ground sewage sludge ash on mortars workability and compressive strength has been studied. An initial decrease of workability is observed when 30 % of Portland cement is replaced by original ash. When ash grinding time increases a little increased of workability is observed. Mortars containing a 15 % of ash cured at 40°C for 14 and 28 days showed equal or higher compressive strength than control mortar. No significative differences sere observed among mortars containing ash with different grinding times.

Improvement of Portland Cement/Fly Ash Mortars Strength Using Classified Fly Ashes

The effect of replacing 30 % of portland cement by Spanish fly ash (class F according to ASTM 0618) and their sized fractions, obtained using sieves on compressive and flexural strength of mortars was studied. The study reveals an enhancement of Ri/Rc and Ri/Rf ratios when finest fly ash fraction is used due to pozzolanic effect. This pozzolanic effect is related with fly ash fineness, but not in the same way for compressive and flexural strength.

Ground Fly Ashes: Characteristics and their Influence on Fresh and Hardened Mortars

Abstract A fly ash was mechanically treated by grinding, yielding ground samples with different fineness. During grinding, calcium carbonate formation was observed. Workability of mortars containing 30% ground fly ash replacing Portland cement is similar (10 minutes-grinding sample) or less (20–60 minutes-grinding samples) than “as received” fly ash one, due to loss of spherical shape of particles; however, in all cases, they showed greater workability than “only Portland cement” mortars. Compressive and flexural strength development at early ages of specimens cured at 20 °C showed that there is an important influence of fly ash fineness: compressive and flexural strengths increased with grinding-time.