THE HYDRATION OF THE ALUMINATES OF CALCIUM: IV. HYDROTHERMAL REACTIONS OF TRICALCIUM ALUMINATE AND ITS HYDRATES

1943 ◽  
Vol 21b (4) ◽  
pp. 65-72 ◽  
Author(s):  
G. M. Harris ◽  
W. G. Schneider ◽  
T. Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Rectangular Plate ◽  
Hydrothermal Treatment ◽  
Saturated Steam ◽  
Partial Hydrolysis ◽  
Portland Cement Concrete ◽  
Steam Curing ◽  
Hydrated Alumina ◽  
Hydrothermal Reactions ◽  
Tricalcium Aluminate

A study was made of the hydrothermal reactions of tricalcium aluminate and its hydrates between 120° and 350 °C. Homogeneous samples of the hexahydrate of tricalcium aluminate may be prepared by treatment of the aluminate or its hexagonal hydrate in saturated steam at temperatures up to 150 °C. At temperatures of 250 °C. and above, under conditions favouring rapid hydrolysis, such as the addition of water to the anhydrous aluminate or hydroaluminate before autoclaving and rapid elevation of the temperature of the autoclave, crystals of calcium hvdroxide and of a hydroaluminate of lower lime–alumina ratio appear, usually mixed with the isometric hexahydrate. The new hydroaluminate occurs as rectangular, elongated, prismatic plates of low birefringence, refractive index 1.627, and has a lime–alumina ratio probably lower than 1.5. The hexagonal hydrate of tricalcium aluminate gives on hydrothermal treatment a better yield of the low-limed hydroaluminate than does the anhydrous aluminate. Only partial hydrolysis of the hexahydrate was obtained under any of the conditions used, but the hexagonal hydrate, autoclaved for 12 hr. at 350 °C., gave products composed almost entirely of the rectangular plate hydroaluminate and calcium hydroxide. No free hydrated alumina was found in the hydrothermal products.The rectangular plate hydroaluminate of calcium may also be prepared by the action of calcium hydroxide on hydrated alumina in saturated steam at 350 °C. It is therefore a stable product under those conditions.At temperatures below 250 °C. birefringent crystalline material is also formed on autoclaving tricalcium aluminate or its hydrates under conditions favouring hydrolysis. The experimental evidence indicates that one of the products is the birefringent calcium hydroaluminate formed on autoclaving the lower calcium aluminates at temperatures of 105 to 150 °C. (5).Precast Portland cement concrete products, when subjected to steam-curing, normally contain an excess of water, and the conditions for the formation of these birefringent hydroaluminates of calcium are therefore present. The same applies to the commercial steam-curing of other materials containing free lime and hydrated alumina. The formation of these hydroaluminates may explain the peculiar effect on the tensile and compressive strength of mortar and concrete test pieces produced by hydrothermal treatment at temperatures above 150 °C. (9).

THE HYDRATION OF THE ALUMINATES OF CALCIUM: V. THE HYDROTHERMAL DECOMPOSITION PRODUCTS OF TRICALCIUM ALUMINATE AT 350 °C.

1943 ◽  
Vol 21b (11) ◽  
pp. 236-246 ◽  
Author(s):  
Herbert Johnson ◽  
Thorbergur Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Saturated Steam ◽  
Rectangular Plates ◽  
Hydrated Alumina ◽  
Decomposition Products ◽  
Factors Affecting ◽  
X Ray ◽  
Crystalline Product ◽  
Tricalcium Aluminate ◽  
Lower Temperature

When tricalcium aluminate is treated in saturated steam at 350 °C. hydrolysis occurs with the formation of a crystalline product of the composition 4CaO.3Al2O3.3H2O and calcium hydroxide. The same products result when a 3:1 mixture of calcium hydroxide and hydrated alumina are similarly treated. The calcium hydroxide as well as any hexahydrate of tricalcium aluminate formed at lower temperature may be removed from the hydrothermal product by extraction with a solution of acetic acid buffered with calcium acetate.The 4:3:3 calcium hydroaluminate crystallizes in colourless elongated rectangular plates with parallel extinction, positive elongation, and low birefrigence. The average refractive index is close to 1.627 and the density 2.71 (at 20 °C). The crystals are probably orthorhombic.Appreciable dehydration of the product does not occur on heating below 475° to 500 °C. Dehydration between 650° and 750 °C. in a stream of dry air appears to produce decomposition with the liberation of free alumina and probable formation of the product 12Ca0.7Al2O3.The factors affecting the yield of the 4:3:3 calcium hydroaluminate and the mechanism of the hydrothermal reactions of tricalcium aluminate and its hydrates are discussed. Readings of X-ray powder patterns of the 4:3:3 hydroaluminate and its dehydration products are given.

THE HYDRATION OF THE ALUMINATES OF CALCIUM: III. THE HYDRATION OF THE 5:3, 1:1, AND 3:5 CALCIUM ALUMINATES

1943 ◽  
Vol 21b (2) ◽  
pp. 34-42 ◽  
Author(s):  
W. G. Schneider ◽  
T. Thorvaldson
Keyword(s):  
Refractive Index ◽  
Water Absorption ◽  
Anisotropic Material ◽  
Quantitative Estimation ◽  
Saturated Steam ◽  
Hydrated Alumina ◽  
Tricalcium Aluminate ◽  
Calcium Aluminates ◽  
End Products ◽  
Rapid Hydrolysis

The hydration of the aluminates of calcium in saturated steam at 150° and 105 °C. was studied. A method was developed for the quantitative estimation of chemically combined and free hydrated alumina in steam treated mixtures. The rates of hydration at 150 °C. of all the aluminates of calcium were compared. At 150 °C., when conditions favouring- rapid hydrolysis are avoided, the 1:1 and 3:5 lime aluminates are apparently transformed almost quantitatively to the cubic hexahydrate of tricalcium aluminate and hydrated alumina approaching the composition of the monohydrate. The steam treated 5:3 lime aluminate gives lower water absorption and higher content of combined alumina than called for by the above end-products, indicating the formation of a less highly hydrated aluminate of lower lime–alumina ratio than the hexahydrate of tricalcium aluminate. This conclusion is supported by the presence in this product of some anisotropic material with an average refractive index of 1.58. The hydrothermal products obtained on treatment of the three aluminates at 105 °C. all contained larger amounts of this birefringent material and apparently a greater proportion of combined alumina.

THE HYDRATION OF DICALCIUM SILICATE AND TRICALCIUM SILICATE

1936 ◽  
Vol 14b (1) ◽  
pp. 20-30 ◽  
Author(s):  
N. B. Keevil ◽  
T. Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Tricalcium Silicate ◽  
Dicalcium Silicate ◽  
Crystalline Hydrate ◽  
Saturated Steam ◽  
Partial Hydrolysis ◽  
Hydration Products ◽  
X Ray Diffraction ◽  
Constant Weight ◽  
X Ray

Samples of β-dicalcium silicate, γ-dicalcium silicate, tricalcium silicate, hillebrandite and dehydrated hillebrandite were exposed to saturated steam at temperatures between 50° and 375 °C. After drying to constant weight (usually over calcium oxide) the increase in weight and the amount of free calcium hydroxide were determined. Microscopic examinations and X-ray diffraction patterns of the products were made. The hydration products were then dehydrated and similar studies of the products made. The hydrolysis of the hydration products also was studied.It was found that between 110° and 350 °C. β- and γ-dicalcium silicates may absorb water without hydrolysis to form three crystalline products. Two of these are identical with products already described (20); the third product appears to possess another characteristic crystalline structure as shown by the X-ray pattern, but to have a variable water content with a limiting composition of 2CaO∙SiO2∙H2O. The hydration product may be dehydrated without the liberation of lime.When conditions favoring hydrolyses are avoided, tricalcium silicate hydrates directly to a crystalline hydrate which probably has the limiting composition, 3CaO∙SiO2∙2H2O, although products holding from 1.3 to 2 moles of water give the same X-ray diffraction pattern. When the conditions favor partial hydrolysis, tricalcium silicate decomposes into calcium hydroxide and crystalline hydrated dicalcium silicate. Dehydration of hydrated tricalcium silicate gives one mole of lime along with dicalcium silicate.Hillebrandite exposed to saturated steam at 160 °C. remained unchanged while a sample of dehydrated hillebrandite on hydration gave a product similar to that obtained from β-dicalcium silicate.When treated with a large excess of water, the hydrated silicates hydrolyze to the same extent as the anhydrous silicates, but the final equilibrium is attained more rapidly, especially in the case of hydrated dicalcium silicate.

THE ACTION OF SATURATED STEAM ON DICALCIUM FERRITE AND ON TETRACALCIUM ALUMINOFERRITE

1937 ◽  
Vol 15b (8) ◽  
pp. 331-339
Author(s):  
D. T. Mather ◽  
T. Thorvaldson
Keyword(s):  
Calcium Hydroxide ◽  
Ferric Oxide ◽  
Prolonged Exposure ◽  
Saturated Steam ◽  
X Ray Diffraction ◽  
Similar Treatment ◽  
Rapid Action ◽  
Tricalcium Aluminate ◽  
Water Of Hydration ◽  
Diffraction Patterns

The reactions which occur when dicalcium ferrite and tetracalcium alumino-ferrite are exposed to saturated steam at temperatures between 100° and 300 °C. were studied by determining the water absorbed and the optical properties and X-ray diffraction patterns of the products. The hydration of the probable products of decomposition under the same conditions was also studied. The main results were as follows:Precipitated alumina, treated between 170° and 350 °C. and then dried over calcium oxide or "dehydrite" at 21 °C., gives a monohydrate of alumina. The product is the same whether the initial alumina contains excess combined water or has been dehydrated at any temperature below about 920 °C. On similar treatment between 100° and 170 °C. precipitated ferric oxide loses its water of hydration, giving a material with the crystalline structure of hematite. Tricalcium aluminate at temperatures between 150° and 300 °C. forms the isometric hexahydrate.On prolonged exposure between 100° and 300 °C, dicalcium ferrite is completely decomposed to calcium hydroxide and ferric oxide (hematite). The first step appears to be a rapid direct hydration of the dicalcium ferrite to a dihydrate, followed by a rapid liberation of one mole of calcium hydroxide. Then follows a slow decomposition of the hydrated monocalcium ferrite with the formation of hematite.Similar treatment of tetracalcium aluminoferrite at temperatures from 100° to 300 °C. gives as final products the hexahydrate of tricalcium aluminate, calcium hydroxide, and ferric oxide (hematite). Here again a very rapid action appears to take place, producing the hexahydrate of tricalcium aluminate and hydrated monocalcium ferrite, the latter product then decomposing slowly to calcium hydroxide and ferric oxide as in the case of the dicalcium ferrite.

Low Cement/High Fly Ash Concretes: Their Properties and Response to Chemical Admixtures

1987 ◽  
Vol 113 ◽  
Author(s):  
V. H. Dodson
Keyword(s):  
Fly Ash ◽  
Portland Cement ◽  
Calcium Hydroxide ◽  
Pozzolanic Reaction ◽  
Portland Cement Concrete ◽  
Cement Concrete ◽  
Fly Ashes ◽  
Chemical Admixtures ◽  
Reaction With Water

ABSTRACTIn practice, the amount of fly ash added to portland cement concrete varies depending upon the desired end properties of the concrete. Generally, when a given portland cement concrete is redesigned to include fly ash, between 10 and 50% of the cement is replaced by a volume of fly ash equal to that of the cement. Sometimes as much as twice the volume of the cement replaced, although 45.4 kg (100 lbs) of cement will only produce enough calcium hydroxide during its reaction with water to react with about 9 kg (20 lbs) of a typical fly ash. The combination of large amounts of certain fly ashes with small amounts of portland cement in concrete has been found to produce surprisingly high compressive strengths, which cannot be accounted for by the conventional “pozzolanic reaction”. Ratios of cement to fly ash as high as 1:15 by weight can produce compressive strengths of 20.7 MPa (3,000 psi) at I day and over 41.4 MPa (6,000 psi) at 28 days. Methods of identifying these “hyperactive” fly ashes along with some of the startling results, with and without chemical admixtures are described.

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