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1963
Studies on Tobermorite-Like Calcium Silicate Hydrates : Technical Paper Sidney Diamond
[email protected]
William Lee Dolch Joe L. White
Recommended Citation Diamond, S., W. L. Dolch, and J. L. White. Studies on Tobermorite-Like Calcium Silicate Hydrates : Technical Paper. Publication FHWA/IN/JHRP-63/33. Joint Highway Research Project, Indiana Department of Transportation and Purdue University, West Lafayette, Indiana, 1963. doi: 10.5703/ 1288284313642. This document has been made available through Purdue e-Pubs, a service of the Purdue University Libraries. Please contact
[email protected] for additional information.
STUDIES ON TOBERMORITE-LIKE CALCIUM SILICATE HYDRATES
»
Technical Paper STUDIES ON TOBERMORITE-LIKE CALCIUM SILICATE HYDRATES
TO:
K. B. Woods, Director Joint Highway Research Project
Octoher 31, 19&3
Joint Highway Research Project
File: M>-9 Project: C-36-47I
The technical paper attached entitled "Studies on Tobermorite-Like Calcium Silicate Hydrates" by Sidney Diamond, W. L„ Dolch, and Joe L. White is submitted for approval of presentation and publication.. The presentation is proposed to the Annual Meeting of the Highway Research Board in Washington D»C, in January 196^. Publication would be by that organization e.
The paper is a part of the investigation known as "Calcium Silicate Hydrates" which was conducted by the Joint Highway Research Project utilizing HPS funds o The material is taken from the Final Report on this project which has been submitted for review and acceptance. In the event that approval for presentation has not been received by the date of presentation, the presentation will include a statement that review of the paper has not been made by the ISHC or the BPR„ This is the second paper which has been prepared from this research and which has been submitted for review* A third paper is contemplated and will be submitted upon completion of ito The paper is presented to the Board for approval of presentation and publication
Respectfully submitted,
?/.'/.
??u^£j
Ho Lo Michael, Secretary HIM: be
Attachment Copy: F. L. Ashbaucher J. R. Cooper
w
Lo Dolch
Wo F, F. Go
H. Goetz Fo Havey S. Hill A. Leonards
J. Ro R. M. J. T,n
F, D. E. Bo V. Jo
McLaughlin Miles Mills Scott Smythe Eoder
Digitized by the Internet Archive in
2011 with funding from
LYRASIS members and Sloan Foundation;
Indiana Department of Transportation
http://www.archive.org/details/studiesontobermoOOdiam
Technical Paper
STUDIES ON TOB£RUOEITE-LIKE CALCIUM SILICATE HYDRATES
By
Sidney Diamond, Graduate Assistant Wo L B Dolch, Research Associate Joe L. White, Professor of Agronomy Joint Highway Research Project Project: File:
C-36-47I 4-6-9
Prepared as Part of an Investigation Conducted by
Joint Highway Research Project Engineering Experiment Station Purdue University
in cooperation with Indiana State Highway Commission and the
Bureau of Public Roads
U S Department oi'Qommve Not Reviewed By
Not Released for Publication
Indiana State Highway Commission or the Bureau of Public Roada
Subject to Change
Purdue University Lafayette, Indiana October 31, 1963
STUDIES ON TOBERMORITE-LIKE CALCIUM SILICATE HYDRATES
ABSTRACT
Parallel studies were carried out on certain characteristics of CSH(l) synthesized at room temperature and on CSH(gel) produced by paste or bottle hydration of
p
-C^S, C_S and alite.
Instrumental
methods employed included x-ray diffraction, DTA, infrared spectroscopy, and electron microscopy.
Surface areas of the CSll(l) samples were
measured by water vapor adsorption and heats of adsorption were calculated,
Both CSH(l) and CSH(gel) were shown to have a negative
surface charge in the absence of Ca(QH) . p
A method was devised to
measure the cation exchange capacities of these materials, and the exchange capacities measured were the order of 5 "20 meq/lOOg.
The evidence suggests that CSH(gel) is a single, well-defined phase regardless of starting material or mode of hydration, and that 1
CSH(l) has well-defined properties regardless of variations in
composition o
The two phases are difficult to distinguish by x-ray
methods, but can be differentiated by the intensity of the high-
temperature exotherm on DTA, by particle shape as revealed by electron-
microscopic observation, and by the appearance of the main Si-0 vibration band region in infrared spectroscopy.
INTRODUCTION The poorly- crystallized calcium silicate hydrates that resemble the well-^crystallized mineral tobermorite comprise a group of materials
of importance to cement chemists, and are also of theoretical interest.
The present work is an attempt to characterize in detail some of the
properties of two of these phases, CSH(l) and CSH(gel). M tobermorite{G)." is also known as
The latter
The approach employed features
the study of a number of relevant properties of a suite of what is
hoped are representative materials of each kind, prepared in several different ways.
Methods of study include x-ray diffraction, DTA,
electron microscopy, infrared spectroscopy, water vapor— adsorption and several others.
Somewhat parallel studies were carried out with
certain synthetic well-crystallized tobermorites primarily to determine the effects of lattice substitution; these will be reported elsewhere.
Reference to much of the published work in this field is made difficult by the conflicting terminology used in designating the individual phases, and by failure of some workers consistently to
distinguish between tobermorite itself and the several poorly-crystallized phases now recognized.
A brief summary of some of the known properties of these materials will be presented before proceeding to the details of the present study.
Reviews by Taylor (l) and by Brunauer and Greenberg (2) contain
considerable information. CSH(l) is a poorly-crystallized synthetic calcium silicate hydrate
distinct from, but related to, tobermorite.
It can be prepared by
reaction at room temperature, or as a transient phase under hydrothermal
conditions (3)«
The structure is presumably a layer structure related
to that of tobermorite, but details are not known with certainty.
X-ray diffraction patterns display peaks at the positions of the strong (hkO) lines of tobermorite; a diffuse basal spacing is sometimes observed in the range from about 10A to about l4A, depending on the state of
hydration and on the Ca:Si ratio of the particular material (l). CSH(l) specimens showing similar x-ray patterns have been prepared in
-
3
-
which the Ca:Si ratio may vary from 0.8 to about 1.5.
The DXA pattern
of CSH(l) is characterised by a strong, sharp high- temperature exothermic
peak at about 85O-90O C (h).
Electron microscopy reveals a particle
morphology generally described as consisting of crinkled or crumpled foils; the foils are usually only a few unit layers in thickness (5, 6).
CSH(gel) is produced by paste or bottle hydration of C-S, or by
paste or ball-mill hydration of $»CJ5, under room-temperature conditions (2).
X-ray diffraction shows only three peaks, corresponding to the
positions of the strongest (hkO) lines of tobermorite; basal spacings are not usually observed.
The detailed structure is unknown, but it
is thought to be related to that of tobermorite.
This is a comparatively
high-lime phase with Ca:Si ratio as high as 1.5, and possibly as high as 1.7»
CSH(gel) is usually considered to be mostly straight,
comparatively long fibers, the fibers themselves being composed of rolled up sheets.
An adequate DXA pattern for a pure CSH{gel) phase
has not previously been published, although partial information is
available (2).
Bottle hydration of 0»Q S is said to give rise to a distinct phase called CSH(lX) (7). which may also be formed on extended reaction of C-S in supersaturated lime solution (8), as an initial product in
hydrothermal reaction (3) and, reportedly, by reaction of calcium glycerate solution with silica gel (9)*
CSH(ll) is a lime-rich phase
with Cat Si ratio of 1.5-2*0; thus its composition overlaps that of CSH(gel).
In contrast to the latter, an x-ray basal spacing of about
10A is generally recorded (l).
It has been suggested that this phase
can be identified among calcium silicate hydrates by an x-ray peak at I.56A (10).
Again, the detailed structure is unknown.
The morphology
.
is fibrous; sometimes cigar-shaped bundles of fibers of distinctive
appearance are observed (5, 7).
The DTA pattern is marked by an
exothermic bulge at intermediate temperatures and by a relatively small high- temperature peak in the 85O C region (h)
PREPARATION OF SAMPLES CSH(I)
Seven samples of CSH(l) were prepared by several methods, all of which involved reactions at room temperature.
Five of these were
made by double decomposition reactions, and two were made by direct synthesis from lime and silica.
Four samples were prepared in the same general manner, in which
solutions of sodium silicate and a calcium salt were poured simultaneously into a third container and vigorously stirred, the calcium silicate
hydrate precipitating as large white floes
.
The sodium silicate used
was 0.5 M in each instance; the calcium salt solution used was 0.5 CaCl 9 in one sample, 0.5
M Ca(NO
)
in the others.
M
The molar ratios
of Ca to Si were 1.0 for the sample prepared with CaCl
and one of the
samples made with Ca(N0_)_, and 1.5 and 2.0 respectively for the other two samples made with Ca(N0-)_.
After precipitation the products were
diluted with distilled water, filtered over suction, washed several times, first with water, then with acetone, and finally with ether,
and then dried at 110 C.
A fifth sample was prepared by a more elaborate procedure, devised in an effort to promote microscopic homogeneity.
Two 10-ml Luer-lock
syringes were mounted obliquely to each other with their tips almost touching, so that when the two syringes were simultaneously depressed the two fine streams produced were intimately mixed and the combined
-
5 -
droplets produced would fall into a flask mounted below the syringes.
The contents of the flask were stirred continuously.
Separate
reservoirs were attached to the two syringes so that they could be
repeatedly refilled without disturbing the arrangement.
Two hundred
ml each of solutions of sodium silicate and calcium nitrate were loaded into the respective reservoirs and mixed by simultaneously depressing the syringes , reloading, and repeating the process.
The concentrations
of the solutions were adjusted to yield a Ca:Si molar ratio of 3*5 to 1, in order to get a high-lime product.
After all the solutions
had been combined, the precipitated material was filtered and washed exhaustively, this time starting with saturated calcium hydroxide solution.
The washing was continued using a water-acetone mixture,
acetone, and finally ether, and then the washed sample was dried at
110 C under vacuum.
Two samples were prepared by direct reaction of a concentrated silica sol (Nalco-Ag 10-22, National Aluminate Company) with reagent-
grade Ga(0R)_.
The first preparation was made by direct addition
of the reagents in 1:1 molar proportion.
The resulting suspension was
diluted with distilled water and transferred to a polyethylene bottle. This was rotated on a roller mill for two days, then allowed to stand
undisturbed for three weeks.
The aged precipitate was then filtered,
the initially cloudy filtrate being recycled until the effluent solution
was clear.
The pH of the filtrate was 10.6, suggesting that all the
free Ca(0H)_ had reacted; consequently the sample was washed once with
water and dried.
A second preparation was made in the same way except
that a Ca:Si ratio of 2:1 was used; here the pH of the recycled and
clarified filtrate was 12-5, indicating that unreacted Ca(OH)
was
.
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6
-
The product was washed with water until the pH dropped
present:.
below 12.3 and x-ray examination disclosed the absence of crystalline
After one additional wash the sample was dried and stored.
Ca(OH) p .
For discussion purposes these samples are designated CSH(l)-l through CSH(l)-7, respectively.
Chemical analyses were carried out
on each of them by standard methods and the conventional compositional formulae determined.
These are given in Table
on preparatory methods.
1,
along with information
Considering that the mole ratio of starting
mixtures varied from 1:1 to 3«5:1> the fact that the observed Ca:Si ratios of the five samples made by double decomposition were all so close to
1
is somewhat unexpected.
In contrast, the CSH(l)-7 sample,
prepared by direct synthesis and aged prior to washing and drying,
had a Ca:Si ratio of almost 1.6:1.
Despite the fact that this ratio
is slightly higher than the upper limit normally ascribed to CSH(l),
this sample appears to be CSH(l) rather than CSH(ll), as will be made
clear later
CSHfeel)
CSE(gelJ samples were prepared by hydration of p-C S, C_S and alite.
Well-characterized samples of these cement compounds were
kindly contributed by D. L. Kantro and L. E. Copeland of the Portland Cement Association, and a second sample of alite of somewhat different
composition was donated by A. Klein of the University of California, Berkeley.
Paste hydration of the #-C S and C~S samples was carried
out at 23 C using a water: solids ratio of 0.7* and the hydration was
allowed to proceed for a period of seven months.
Bottle hydration at
the same temperature was carried out in polyethylene bottles rotated
on a wheel at about 30 rpm; in this case the water: solids ratio was
.
-
-
7
Bottle hydration of thep-C_S and C„S samples was allowed to
9-0.
proceed for six months, and of the alltes for four months.
In all
experiments freshly-boiled distilled water that had been cooled to
below room temperature was used, and the containers were sealed against carbon dioxide penetration.
The designations for the specific samples to be discussed in this paper are given in Table 2.
In addition to the samples listed,
bottle hydration products for an additional sample of C_S and of alite were prepared and examined, but the results were essentially identical to those discussed.
The bottle hydration of C.S and of
alite specimens yielded a hydration product apparently similar in all significant respects to the other hydration products of the cement
minerals, and these products are considered to be CSH(gel) in this
report
CSH(II) Several attempts were made to prepare CSK(ll) by the synthesis
described by Toropov et. al.
(