the performance and mechanism analysis of cement ...2.2.3. microstructure of hardened cement pastes....

$: The Performance and Mechanism Analysis of Cement ...2.2.3. Microstructure of Hardened Cement Pastes. Cement pasteswerepreparedforX-raydiffraction(XRD),thermo-gravimetric analysis (TGA),$
Research ArticleThe Performance and Mechanism Analysis ofCement Pastes Added to Aluminum Sulfate-BasedLow-Alkali Setting Accelerator

Xingdong Lv12 Yan Shi1 Yun Dong1 Zhiyang Gao1 and Beixing Li2

1Changjiang River Scientific Research Institute of Changjiang Water Resources Commission Wuhan 430010 China2State Key Laboratory of Silicate Materials for Architecture Wuhan University of Technology Wuhan 430070 China

Correspondence should be addressed to Xingdong Lv 1115650343qqcom

Received 30 June 2016 Revised 17 October 2016 Accepted 24 October 2016 Published 31 January 2017

Academic Editor Sverak Tomas

Copyright copy 2017 Xingdong Lv et al This is an open access article distributed under the Creative Commons Attribution Licensewhich permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Weproposed a type of low-alkali liquid state setting accelerator namedHLSA it was environmentally friendly product To investigatethe temperature adaptation and cement flexibilities of HLSA the setting time and strength development properties of cement withHLSAwere discussed in this paperThe effects of HLSA on hydration process hydration products andmicrostructure were studiedby means of X-ray diffraction (XRD) thermogravimetric analysis (TGA) scanning electron microscope (SEM) and mercuryintrusion porosimetry (MIP)The results show that four typical 425-grade ordinary Portland cement types with 6ndash8HLSA couldsatisfy the first-grade requirements according to JC477-2005 even at a lower temperature (eg 10∘C) Further the percentage ratioof 28 d compressive strength of cement with 6ndash8 HLSA was over 90 the XRD diffraction peak of AFt integrated area of cementwith 7 HLSA was 3818 at 5min of hydration SEM observation revealed that AFt crystals were filled in the pore of cement at 28 dof hydration the temperature adaptation and cement flexibilities of HLSA were excellent the cement with HLSA coagulating in ashort time attributed to promoting the formation of abundant AFt and the hydration of C3S

1 Introduction

Shotcrete is a kind of concrete which is conveyed underpressure through a pneumatic hose or pipe and projectedinto place at high velocity with simultaneous compactioncondensation and hardening [1 2]The shotcrete can acquirehigh early age strength and coagulate in a short time [3] itis often used for hydraulic engineering slope engineeringemergency rescue and repairing engineering [4 5] Thesetting accelerator is an essential component of shotcreteThe development of setting accelerator was dated back to thenineteen-thirties the setting accelerators were mainly pow-der accelerators at the early stage of developmentThepowderaccelerators easily lead to problems of dust pollution dispers-ing unevenly and high energy consumption in constructionprocess Meanwhile it is harmful to construction crewsrsquohealth at some degrees in dry spray of construction processWith the developing of wet sprayed technology of shotcreteliquid setting accelerators emerged in nineteen-eighties [6]

The liquid setting accelerators can avoid the problems ofdust pollution and uneven dispersing caused by powderaccelerators in dry spray process The main chemical com-ponents of traditional setting accelerators are classified as(1) sodium silicates-based such as water glass and modi-fied sodium silicate (2) aluminate-based such as sodiumaluminate potassium aluminate and aluminum sulfate (3)carbonate and hydroxide-based such as sodium carbonateand sodium hydroxide [7] The common problems thatexisted was that the alkali content of the liquid and powdersetting accelerators were very high at the early research stageof setting accelerators The high alkali setting acceleratorscould easily lead to the following problems (1) increasingthe risk of alkali-aggregate reaction in concrete (2) beingharmful to the buildersrsquo health with extremely high pH level(3) a severe reduction of the shotcrete long-term mechanicalproperties [8] According to EN 934-5 [9] the low-alkalisetting accelerators are defined as setting accelerators whosealkali metal content (sodium and potassium) expressed as

HindawiAdvances in Materials Science and EngineeringVolume 2017 Article ID 8906708 10 pageshttpsdoiorg10115520178906708

2 Advances in Materials Science and Engineering

Table 1 Chemical composition of cement (w)

Cement SiO2 CaO Al2O3 Fe2O3 MgO SO3 R2O LossH 2349 5824 600 281 235 239 076 306Y 2102 6238 480 368 103 202 060 378

Table 2 Main chemical composition of HLSA (w)

Sample Al2O3 SO3 Na2O Fminus LossHLSA 843 1982 504 321 6015

equivalent of Na2O+ 0658K2O is not above 8 bymassThe low-alkali setting accelerators have some significantadvantages Therefore the preparation of low-alkali settingaccelerators has been themain trend and hot topic in this field[10]

The setting accelerators consist of many types and theacceleration mechanism is not conclusive the present theo-ries of acceleration mechanism are as follows (1) the forma-tion of abundantAFt in a short time of the setting acceleratorsbased on aluminate A large amount of SO4

2minus from settingaccelerator can react with aluminate hydration products ofcement to form AFt and high reactive secondary gypsumThe AFt crystals are connecting reticular structure in cementpastes the formation of cement hydration products especiallycalcium aluminate hydrate needs to combine free waterleading to cement condensation in a short time [11] and (2)the formation of abundant hydrated calcium aluminate of thesetting accelerators based on carbonate and sodium silicatesDue to the obvious decrease of gypsum concentration theretard effect of gypsum isweakened and even vanishedwhichpromotes the hydration of C3A to form cubic crystal C3AH6in a short timeThenmassive heat is released at the same timeand the cement paste is setting rapidly [12]

However the effects of different setting accelerators addi-tion on cement were also different meanwhile the variationof hydration products mass percentage of cement containingsetting accelerators was rarely studied As a result the alu-minum sulfate-based low-alkali liquid state setting accelera-tor named HLSA has been prepared in laboratory HLSA wasenvironmentally friendly product it could avoid damagingthe crewsrsquo health and decrease the energy consumption inconstruction process The properties of setting time andstrength development of cement in addition to HLSA wereinvestigated The effects of HLSA on hydration processhydration products and microstructure were investigatedby means of X-ray diffraction (XRD) thermogravimetricanalysis (TGA) scanning electron microscope (SEM) andmercury intrusion porosimetry (MIP)

2 Experimental

21 Raw Materials The cement used was two typical 425-grade ordinary Portland cement types which were manufac-tured by Yadong (Y) Cement Company Ltd (Wuhan Hubei)and Huaxin (H) Cement Company Ltd (Wuhan Hubei)

respectivelyThe Portland cement blended with less than 20mineral admixtures The physical and chemical properties ofPortland cement all satisfied China National Standard GB175-2007 the chemical composition of cement was shown inTable 1

TheHLSAprepared in labwere synthesized by industrial-grade aluminum sulfate (Al2(SO4)3sdot18H2O) chemically puresodium fluoride (NaF) chemically pure triethanola-mine ((HOCH2CH2)3N) chemically pure polyacrylamide(-[CH2CH]119899CONH2-) and chemically pure phosphoricacid (H3PO4) The industrial-grade aluminum sulfate wasobtained from the Zibo Guangzheng Aluminum Salt Chemi-cal Industry Co Ltd (Zibo Shandong) The chemicallypure sodium fluoride triethanolamine polyacrylamide andphosphoric acid were obtained from Sinopharm

HLSAwas light green homogeneous liquid in appearancewith density of 161 gcm3 and solid content of 405 Thealkali content expressed as equivalent of Na2O + 0658times K2O was 50 which belongs to low-alkali settingaccelerator The main chemical composition of HLSA wasshown in Table 2

22 Experimental Methods

221 Cement Setting Time The setting time of cement withHLSAwasmeasured according toChinese BuildingMaterialsStandards JC 477-2005 with water to cement ratio (WC)040 the dosage of setting accelerator was 6 7 and 8 (bymass of cement) respectively The cement pastes were curedunder the condition of temperature 20 plusmn 2∘C and RH not lessthan 90The effect of HLSA on cement setting time at 10∘Cand 20∘Cwas investigated respectively it used Yangdong PsdotO425 Portland cement and Huaxin PsdotO 425 Portland cementand the composition mix was shown in Table 3

222 Strength Development of CementMortar Themeasure-ment of cement mortar strength development was accordingto Chinese Building Materials Standards JC 477-2005 Withstandard sand cement water ratio of 3 2 1 the additionof setting accelerator was 6 7 and 8 (by mass ofcement) respectively Cementmortar specimenswere 40mmtimes 40mmtimes 160mmprismsThe specimenswere prepared andcured in molds for 24 h under the condition of temperature20 plusmn 2∘C and RH over 90 then they were demouldedand tested for 1 d compressive strength immediately the

Advances in Materials Science and Engineering 3

Table 3 Mix proportions of cement paste

Types WC Cement type Temperature∘C DosageY10-S6 04

Yangfang PsdotO 425

106

Y10-S7 04 7Y10-S8 04 8Y20-S6 04

206

Y20-S7 04 7Y20-S8 04 8H10-S6 04

Huaxin PsdotO 425

106

H10-S7 04 7H10-S8 04 8H20-S6 04

206

H20-S7 04 7H20-S8 04 8

percentage of mortar in addition to HLSA compressivestrength growth at 1 d was characterized by the following

1198621 () = 100 times119862(1198861) minus 119862(1198871)119862(1198871)

() (1)

where 1198621() was growth rate of compressive strength at1 d 119862(1198861) were compressive strength of specimens containingHLSA at 1 d and 119862(1198871) were compressive strength of blankspecimens at 1 d

The rest of specimens were cured under the conditionof air temperature 20 plusmn 2∘C and RH not less than 90The retention percentage of compressive strength at 28 d wascharacterized by the following

11986228 () = 100 times119862(11986728)119862(11986128)() (2)

where 11986228() was retention percentage of compressivestrength at 28 d 119862(11986728) were compressive strength of speci-mens containing HLSA at 28 d and 119862(11986128) were compressivestrength of blank specimens at 28 d

223 Microstructure of Hardened Cement Pastes Cementpastes were prepared for X-ray diffraction (XRD) thermo-gravimetric analysis (TGA) scanning electron microscope(SEM) and mercury intrusion porosimetry (MIP) analyseson water to cement ratio 040 in addition to 7 HLSAThe hydration of hardened cement pastes was stopped afterpredetermined curing age by breaking test block into smallpieces in absolute ethyl alcohol The small samples wereground into powders with particle size less than 80 120583m byagate grinding for XRD and TGA analysesThe small sampleswith particle size range from 5mm to 8mm were selectedfor SEM analyses Fresh paste was cast into capsules (3mmdiameter 45mm height) cured under water and stored at20∘C At required time of hydration a slice (2mm thick) ofhardened paste was cut for MIP analyses

XRD was employed to identify the cement hydrationphase The XRD data were collected by Bruker D8 advancediffractometer with a 3KW Cu K120572 radiation and the X-ray

tube was operated at 40 kV and 40mA The scanning speedof XRD was 10∘min The software MDI Jade 65 was usedto study the special diffraction peak of ettringite and CHfor quantitative phase analyses [13] TG analysis was usedto test the weight loss and decomposition temperature ofphase All samples were tested within the range of 25∘C to800∘C using a differential thermal analyzer (STA449C fromNetzsch Germany) under air atmosphere with a scanningrate of 15∘Cmin The field emission electron microscopy(Ultra Plus-43-13 from Zeiss Germany) was used to observemorphology and microstructure of cement pastes MIP mea-surement was carried out on micromeritics instrument cor-poration AutoPore IV 9500 mercury scanning porosimeterwith maximum pressure 228MPa and its measurable poresize ranges from 3 nm to 1000 um

In order to investigate the amount of cement hydrationproducts in addition to HLSA Method of semiquantitativeanalysis was used to study the diffraction peak characteristicsof hydration products AFt and Ca(OH)2 (CH) by softwareJade 6 DTG curves clearly showed the relationship betweentemperature and weight loss in case the weight loss was closeThe decomposition peak of CH occurred between 420 and460∘C in DTG curves the amount of CH could be calculatedby the following formula

CH () =WLCH ()MWCHMWH

2O (3)

where WLCH() corresponds to the weight loss of CH inpercent andMWCH andMWH

2O were the molecular weights

of portlandite and water respectively [14]

3 Results and Discussion

31 Temperature Adaptation Temperature was an importantexternal factor affecting chemical reaction rate The tem-perature of concrete raw materials was changeable whenthe regions seasons and daily temperature changed so itshould pay attention to the problems caused by the change-able temperature in construction process [15] In order toinvestigate the effect of HLSA on cement setting time at


InitialFinal

Y10-

S6

Y10-

S8

Y10-

S7

Y20-

S7

Y20-

S8

Y20-

S6

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(a) Y

InitialFinal

H20

-S6

H20

-S8

H10

-S8

H10

-S6

H10

-S7

H20

-S7

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(b) H

Figure 1 Effect of setting time of cement in addition to HLSA at 10∘C and 20∘C

InitialFinal

C1

C28

28 27 26

63

4 37

6 8Dosage of setting accelerator ()

7

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

Setti

ng ti

me (

min

)

30

40

50

60

70

80

90

100

(a) Y

InitialFinal

C1

C28

3 28 27

69

545


740

50

60

70

80

90

100

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

8

Setti

ng ti

me (

min

)

(b) H

Figure 2 Effect of setting time and strength development of two kinds of cement containing HLSA

different environment temperature the tunnel temperature ofsummer and winter was simulated in labThe effect of settingtime of cement in addition to HLSA at 10∘C and 20∘C wasinvestigated the results were shown in Figure 1

The cement setting time was shortened as the curingtemperature was higher at the same dosage The setting timeof cement in addition to 6 HLSA could meet first-graderequirement according to Chinese Building Materials Stan-dards JC 477-2005 at temperature 20∘C The setting time ofcement in addition to 6HLSA could meet acceptable prod-uct requirement according to JC 477-2005 at temperature10∘C It could be supposed that the temperature adaptationof HLSA was excellent as it could maintain the flash settingeffect at lower temperature (eg 10∘C)The setting time couldmeet the first-grade requirement by increasing the dosage ofsetting accelerator at lower temperature

32 Cement Flexibilities Thecement setting time and cementmortar strength development in addition to 6 7 and 8HLSA were investigated the results were shown in Figure 2It was supposed that the adaptation between admixture andcement was good as the concrete or mortars prepared withthe admixture could generate desired performance on thecontrary it could be thought that the adaptation betweenadmixture and cement was not good according to ChineseStandard GB 50119-2013 [16]

The setting time of cement in addition to HLSA atthe dosage range from 6 to 8 could meet the first-grade requirement according to Chinese Building MaterialsStandards JC 477ndash2005 especially cement Y and cement Hwhich could meet first-grade requirement at the dosage 6The higher the dosage was the shorter the setting time wouldbe The compressive strength growth of mortars prepared


Y20-S7

Blank

998771

CH998771

AFt

20 30 40102120579 (

∘)

C3SC2S

(a) 5min

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

AFm998786CH998771

AFt

C3S

C2S

998771

998771

(b) 5 h

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(c) 1 d

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(d) 28 d

Figure 3 XRD patterns of hydrated cement in addition to 7 HLSA

with two cement types at 1 d presented an increasing trendas the dosage increased Compressive strength growths ofmortars prepared with two cement types at 1 d were all above40 at the dosage of 8 it was noted that compressivestrength growth of mortar prepared with cement Y andcement H at 1 d was all above 60 The 28 d retentionpercentage ofmortar compressive strengthwas all above 90which was much higher than the first-grade requirement of75 according to JC 477-2005 It is suggested that HLSAcould avoid the problems of significant strength loss at latestage caused by high alkali content of traditional settingaccelerators Consequently the cement flexibilities of HLSAwere excellent

33 XRD Analysis Figure 3 showed XRD patterns ofhydrated cement with 7 HLSA (Y20-S7) and blank speci-mens at the age of 5min 5 h 1 d and 28 d respectively Theintegrated results of XRDdiffraction peak of AFt correspond-ing to 2120579 range of 90ndash100∘ andCHcorresponding to 2120579 rangeof 170ndash190∘ were shown in Tables 4 and 5 respectively

The Y20-S7 specimen presented intensive diffractionpeak of AFt while the blank specimens never detected diffrac-tion peak of AFt after 5min of hydration it suggested thatY20-S7 specimen had generated AFt at 5min of hydrationThe Y20-S7 specimen diffraction peak integrated area of AFtwas 2520 of the blank specimens at 5 h of hydration TheY20-S7 specimendiffraction peak integrated area ofAFt at 5 hof hydration presented decreasing trend compared to 5minof hydration The XRD curve of Y20-S7 specimen detecteda weak diffraction peak of AFm at 5 h of hydration it waspossible that the AFt partially converted into AFm due to theconcentration of SO4

2minus in pore solution of cement decreasingsharply [17] the chemical reaction occurred

AFt + 2C4AH13 997888rarr 3AFm + 2CH + 20H (4)

(see [18 19])The blank specimen diffraction peak integrated area of

AFt at 1 d of hydration was approximate to the Y20-S7specimen at 5min of hydration It suggested that the amountof AFt of Y20-S7 specimen generated during 5min wasapproximate to the ordinary Portland cement hydration


Table 4 The integrated results of XRD diffraction peak of AFt corresponding to 2120579 range of 90ndash100∘

Specimens Hydration age 119889-value (A) FWHM (∘) Height Area

Blank

5min mdash mdash mdash mdash5h 96494 0175 124 13121 d 96666 0175 343 362628 d 96680 0132 218 1745

Y20-S7

5min 96888 0203 311 38185 h 96884 0150 365 33061 d 96909 0108 497 324028 d 96798 0167 300 3035

Table 5 The integrated results of XRD diffraction peak of CH corresponding at 2120579 range of 170ndash190∘


Blank 1 d 49080 0154 442 412428 d 49033 0149 914 8269

Y20-S7 1 d 49135 0177 196 209828 d 48978 0189 277 3172

5min5h1d28d

200 400 600 8000Temperature (∘C)

(a) Blank

5min5h1d

28d

200 400 600 8000Temperature (∘C)

(b) Y20-S7

Figure 4 DTG curves of hydrated cement

during 1 d The Y20-S7 specimen diffraction peak integratedarea of CH at 1 d and 28 d was 508 and 384 of blankspecimen respectively and the Y20-S7 specimen diffractionpeak integrated area of CH was less than the blank specimenfrom 1 d to 28 d of hydration

34 DTG Analysis The effect of HLSA on cement hydrationproducts was investigated by the means of differential scan-ning calorimetry analysis the results were shown in Figure 4

The weight loss peaks between 0 and 200∘C of DTGcurves were complicated It was generally acknowledged thatAFt C-S-H and gypsum decomposition occurred in thistemperature range However the decomposition peaks of C-S-H andAFt were overlapped [20] Li et al [21] suggested thatthe weight loss at 20ndash80∘C is caused by the decompositionof AFt according to Chang et al [22] the transformation ofCaSO4sdot2H2O to CaSO4sdot05H2O in temperature ranges from80 to 140∘C As Odler et al [19 23] suggested it was possibleto assign the first two peaks at 120 and 145∘C to ettringite and

gypsum decomposition The DTG curve of blank specimenoccurred at intensive decomposition peak of AFt at 5 h ofhydration it is suggested that AFt had already been generatedat that moment The decomposition peak corresponding toAFt of Y20-S7 specimen presented increase at first and thendecrease from 1 d to 28 d of hydration it indicated that AFtwas transformed to AFm at some degrees the results wereconsistent with XRD analysis of Section 33 The CH contentin hydrated cement pastes was demonstrated in Figure 5It suggested CH content of Y20-S7 specimen was less thanthe blank specimen from 1 d to 28 d of hydration again CHcontent of Y20-S7 specimen at 1 d and 28 d was 440 and399 of the blank specimen respectively

35 SEMAnalysis Figure 6 showed scanning electronmicro-scope (SEM) photographs of hydrated cement specimenscontaining 7 HLSA A large amount of AFt and C-S-Hof Y20-S7 specimen was formed at 5min of hydration theneedle-like AFt connected with each other compactly to


Table 6 Parameters and distribution of pore of cement pastes at 1 d and 28 d

Specimens Curing aged Total pore volume(mLsdotgminus1) Porosity Pore size distribution(mLsdotgminus1)3ndash20 nm 20ndash50 nm 50ndash100 nm gt100 nm

Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7

Hydration time 5min 5h 1d 28d

0

2

4

6

8

10

12

CH (

)

Figure 5 CH content in hydrated cement pastes

form reticular structure It was observed that some hexagonalshape portlandite crystals and a little of AFt crystals ofblank specimen were formed at 5 h of hydration SomeAFt crystals of Y20-S7 specimen were still observed at 5 hof hydration however the amount of AFt was decreasingcompared to 5min of hydration meanwhile the hexagonalshape portlandite crystals were unobserved The amorphousC-S-H and AFt crystals were distributed in the cement and afew portlandite crystals were formed of Y20-S7 specimen at1 d of hydrationThe apparentmorphology of blank specimenwas dense and amorphous C-S-H and portlandite crystalsgrew compactly However needle-like AFt and amorphousC-S-H of Y20-S7 specimens grew crisscrossed compactly andAFt crystals were filled in the pore of cement

36 Pore Structure Analysis The cumulative pore volumeof hardened cement paste was considered a main factorto cement pastes mechanical properties It was believedthat strength development of cement paste increased bythe decrease of cumulative pore volume The differentialdistribution curve was calculated from the cumulative porevolume curve [24] according to Wu and Lian [25] the poresof hardened cement pastes were classified as harmless pore(lt20 nm) little harmful pore (20ndash50 nm) and harmful pore(50ndash200 nm) The pore structures of hardened cement weremeasured bymeans ofMIP the results were shown in Table 6The total porosity of Y20-S7 specimenwas less than the blankspecimen at 1 d and 28 d of hydration The pores with porediameter between 3 and 20 nmofY20-S7 specimenwere 66

more than the blank specimen at 1 d of hydration It indicatedthat HLSA could reduce hardened cement paste pore sizeat early age of hydration Meanwhile it was beneficial toimprove the cement mechanical properties at early age Thepores with pore diameter less than 50 nmof Y20-S7 specimenwere 46more than the blank specimen at 28 d of hydrationit showed that HLSA could refine pore structures at somedegrees it is induced to improve retention percentage ofcompressive strength at late age

37 Acceleration Mechanism of HLSA The effect of HLSAon cement hydration products amount was characterizedthat a large amount of crystallization of AFt was formed atvery early age of hydration the amount of AFt crystals wereslightly decreasing at 5 h of hydration however the content ofAFt was still very high at 28 d of hydrationThe content of CHcrystals was lower than the blank specimen from 1 d to 28 dof hydration

Themain components of HLSAwere SO42minus Al3+ and Fminus

When HLSA and cement contacted the following reactionwould be taking place

Ca2+ + Fminus 997888rarr CaF2 darr (5)

2Al3+ + 3SO42minus + 3CH + 6H2O

997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H

997888rarr 3CaO sdot Al2O3 sdot 3CaSO4 sdot 32H2O (AFt)(7)

6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H


CaF2 was formed readily because it was more easilycrystallized than CH The balance of electric double layerof C3S surface was destructed because abundant Ca2+ wasconsumed which led to the formation of the electric doublelayer of C3S difficultly and shortened the induction period ofC3S greatly [26] The Y20-S7 specimen had generated C-S-Hgel at 5min of hydration it suggested that C3S had begun tohydrate at that moment

Equation (6) showed that the free state of Al3+ and SO42minus

readily combined CH in cement to form highly reactive


2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d

Figure 6 Scanning electron microscope (SEM) photographs of hydrated cement specimens


secondary gypsumand secondary gypsum easily reactedwiththe hydration products of C3A to form AFt Equation (8)suggested that aluminum sulfate reacted with CH to formAFt in aqueous alkaline medium at normal temperature Theapproaches of the formation of AFt were extensive it led tothe formation of a large amount of AFt in a short time Thecement with HLSA coagulating in a short time attributedto a large of amount AFt connected reticular structureand distributed uniformly in cement pastes Meanwhile theHLSA shortened induction period of C3S and promoted thehydration of C3S greatly

4 Conclusions

(1) The temperature adaptation and cement flexibilities ofHLSA were excellent The cement setting time couldmeet the first-grade requirements according to JC477-2005when increasing the dosage of 1 at temper-ature 10∘C compared to temperature 20∘CThe settingtime of cement with HLSA at the dosage range from6 to 8 could meet the first-grade requirementsaccording to JC 477-2005 meanwhile the cementretention percentage of compressive strength at 28 dwas all above 90

(2) The Y20-S7 specimen XRD diffraction peak of AFtintegrated area was 3818 however the blank specimenwas 0 at 5min of hydration The Y20-S7 specimendiffraction peak of AFt integrated area was 2520of the blank specimen at 5 h of hydration The CHamount of Y20-S7 specimen was less than the blankspecimen from 1 d to 28 d of hydration HLSA couldreduce hardened cement paste pores size at early ageof hydration and refine the pores structures at somedegrees

(3) The acceleration mechanism of HLSA attributed topromote the hydration of C3A and the formation ofAFt in a short time Meanwhile HLSA could shortenthe induction period of C3S greatly and promote thehydration of C3S

Competing Interests

The authors declare that there is no conflict of interestsregarding the publication of this paper

Acknowledgments

The work described in this paper was supported by theNational Natural Science Foundation of China under Grantnos 51479011 and 51139001

References

[1] J Wang D Niu S Ding Z Mi and D Luo ldquoMicrostructurepermeability andmechanical properties of accelerated shotcreteat different curing agerdquo Construction and Building Materialsvol 78 pp 203ndash216 2015

[2] J-P Won U-J Hwang C-K Kim and S-J Lee ldquoMechanicalperformance of shotcrete made with a high-strength cement-basedmineral acceleratorrdquoConstruction andBuildingMaterialsvol 49 pp 175ndash183 2013

[3] J Wang D Niu and Y Zhang ldquoMechanical properties perme-ability and durability of accelerated shotcreterdquoConstruction andBuilding Materials vol 95 pp 312ndash328 2015

[4] C Maltese C Pistolesi A Bravo F Cella T Cerulli andD Salvioni ldquoA case history effect of moisture on the settingbehaviour of a Portland cement reacting with an alkali-freeacceleratorrdquo Cement and Concrete Research vol 37 no 6 pp856ndash865 2007

[5] C K Y Leung R Lai and A Y F Lee ldquoProperties of wet-mixed fiber reinforced shotcrete and fiber reinforced concretewith similar compositionrdquo Cement and Concrete Research vol35 no 4 pp 788ndash795 2005

[6] C Snyder Raymond and F Snyder Paul Liquid concreteaceleratormixtures andmethods for use thereof USA 4046584September 1997

[7] S A Austin and P J Robins Sprayed Concrete Properties Designand Application McGraw-Hill London UK 1995

[8] L R Prudencio Jr ldquoAccelerating admixtures for shotcreterdquoCement and Concrete Composites vol 20 no 2-3 pp 213ndash2191998

[9] EN 934-5 Admixture for Sprayed Concrete-DefinitionsRequirements Conformity Marking and Labelling StandardsPolicy and Strategy Committee 2007

[10] Z Pan X Wang and W Liu ldquoProperties and accelerationmechanism of cement mortar added with low alkaline liquidstate setting acceleratorrdquo Journal Wuhan University of Technol-ogy Materials Science Edition vol 29 no 6 pp 1196ndash1200 2014

[11] X Xin and D Qingjun ldquoSummary of cement rapid-settingadition and their mechanism researchesrdquo Journal of WuhanUniversity of Technology vol 21 no 1 pp 28ndash30 1999

[12] L Chen L Shizong W Yanrong and Y Bilan ldquoStudy on theaccelerating mechanism of accelerators in concreterdquo Journal ofBuilding Materials vol 3 no 2 pp 175ndash181 2000

[13] R Wang X-G Li and P-M Wang ldquoInfluence of polymer oncement hydration in SBR-modified cement pastesrdquo Cement andConcrete Research vol 36 no 9 pp 1744ndash1751 2006

[14] A Peschard A Govin P Grosseau B Guilhot and R Guyon-net ldquoEffect of polysaccharides on the hydration of cement pasteat early agesrdquo Cement and Concrete Research vol 34 no 11 pp2153ndash2158 2004

[15] C Paglia FWombacher andH Bohni ldquoThe influence of alkali-free and alkaline shotcrete accelerators within cement systemsinfluence of the temperature on the sulfate attack mechanismsand damagerdquo Cement and Concrete Research vol 33 no 3 pp387ndash395 2003

[16] S Zhenping J Zhengwu and W Peiming ldquoMeasures toimprove compatibility between concrete admixtures andcementrdquo Journal of Building Materials vol 6 no 4 pp404ndash409 2003

[17] D Niu J Wang and Y Wang ldquoEffect of hydration aging andwater binder ratio onmicrostructure andmechanical propertiesof sprayed concreterdquo Journal Wuhan University of TechnologyMaterials Science Edition vol 30 no 4 pp 745ndash751 2015

[18] Y Runzhang Cementitious Materials Science Wuhan Univer-sity of Technology Press Wuhan China 2006

[19] I Odler and S Abdul-Maula ldquoPossibilities of quantitative deter-mination of the AFt-(ettringite) and AFm-(monosulphate)


phases in hydrated cement pastesrdquo Cement and ConcreteResearch vol 14 no 1 pp 133ndash141 1984

[20] W Prince M Espagne and P-C Aitcin ldquoEttringite formationa crucial step in cement superplasticizer compatibilityrdquo Cementand Concrete Research vol 33 no 5 pp 635ndash641 2003

[21] G Li T He D Hu and C Shi ldquoEffects of two retarders onthe fluidity of pastes plasticized with aminosulfonic acid-basedsuperplasticizersrdquo Construction and Building Materials vol 26no 1 pp 72ndash78 2012

[22] H Chang P J Huang and S C Hou ldquoApplication of thermo-Raman spectroscopy to study dehydration of CaSO4sdot2H2O andCaSO4sdot05H2OrdquoMaterials Chemistry and Physics vol 58 no 1pp 12ndash19 1999

[23] J Bensted and S P Varma ldquoSome applications of infrared andRaman spectroscopy in cement chemistry Part 3 Hydration ofportland cement and its constituentsrdquo Cement Technology vol5 no 5 pp 5440ndash5450 1974

[24] E Berodier and K Scrivener ldquoEvolution of pore structure inblended systemsrdquo Cement and Concrete Research vol 73 pp25ndash35 2015

[25] Z Wu and H Lian High Performance Concrete Railway Pub-lishing House Beijing China 1999

[26] J Wang J Song K Liu and D Wang ldquoStudy on the lowalkali liquid flash setting admixture of aluminum sulfate forshotcreterdquo Concrete vol 302 no 12 pp 84ndash87 2014

Submit your manuscripts athttpswwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of



CeramicsJournal of


CompositesJournal of

NanoparticlesJournal of



International Journal of

Biomaterials


NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of


The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014


CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research



MetallurgyJournal of


BioMed Research International

MaterialsJournal of


Nano

materials


Journal ofNanomaterials


Table 1 Chemical composition of cement (w)

Cement SiO2 CaO Al2O3 Fe2O3 MgO SO3 R2O LossH 2349 5824 600 281 235 239 076 306Y 2102 6238 480 368 103 202 060 378

Table 2 Main chemical composition of HLSA (w)

Sample Al2O3 SO3 Na2O Fminus LossHLSA 843 1982 504 321 6015

equivalent of Na2O+ 0658K2O is not above 8 bymassThe low-alkali setting accelerators have some significantadvantages Therefore the preparation of low-alkali settingaccelerators has been themain trend and hot topic in this field[10]

The setting accelerators consist of many types and theacceleration mechanism is not conclusive the present theo-ries of acceleration mechanism are as follows (1) the forma-tion of abundantAFt in a short time of the setting acceleratorsbased on aluminate A large amount of SO4

2minus from settingaccelerator can react with aluminate hydration products ofcement to form AFt and high reactive secondary gypsumThe AFt crystals are connecting reticular structure in cementpastes the formation of cement hydration products especiallycalcium aluminate hydrate needs to combine free waterleading to cement condensation in a short time [11] and (2)the formation of abundant hydrated calcium aluminate of thesetting accelerators based on carbonate and sodium silicatesDue to the obvious decrease of gypsum concentration theretard effect of gypsum isweakened and even vanishedwhichpromotes the hydration of C3A to form cubic crystal C3AH6in a short timeThenmassive heat is released at the same timeand the cement paste is setting rapidly [12]

However the effects of different setting accelerators addi-tion on cement were also different meanwhile the variationof hydration products mass percentage of cement containingsetting accelerators was rarely studied As a result the alu-minum sulfate-based low-alkali liquid state setting accelera-tor named HLSA has been prepared in laboratory HLSA wasenvironmentally friendly product it could avoid damagingthe crewsrsquo health and decrease the energy consumption inconstruction process The properties of setting time andstrength development of cement in addition to HLSA wereinvestigated The effects of HLSA on hydration processhydration products and microstructure were investigatedby means of X-ray diffraction (XRD) thermogravimetricanalysis (TGA) scanning electron microscope (SEM) andmercury intrusion porosimetry (MIP)

2 Experimental

21 Raw Materials The cement used was two typical 425-grade ordinary Portland cement types which were manufac-tured by Yadong (Y) Cement Company Ltd (Wuhan Hubei)and Huaxin (H) Cement Company Ltd (Wuhan Hubei)

respectivelyThe Portland cement blended with less than 20mineral admixtures The physical and chemical properties ofPortland cement all satisfied China National Standard GB175-2007 the chemical composition of cement was shown inTable 1

TheHLSAprepared in labwere synthesized by industrial-grade aluminum sulfate (Al2(SO4)3sdot18H2O) chemically puresodium fluoride (NaF) chemically pure triethanola-mine ((HOCH2CH2)3N) chemically pure polyacrylamide(-[CH2CH]119899CONH2-) and chemically pure phosphoricacid (H3PO4) The industrial-grade aluminum sulfate wasobtained from the Zibo Guangzheng Aluminum Salt Chemi-cal Industry Co Ltd (Zibo Shandong) The chemicallypure sodium fluoride triethanolamine polyacrylamide andphosphoric acid were obtained from Sinopharm

HLSAwas light green homogeneous liquid in appearancewith density of 161 gcm3 and solid content of 405 Thealkali content expressed as equivalent of Na2O + 0658times K2O was 50 which belongs to low-alkali settingaccelerator The main chemical composition of HLSA wasshown in Table 2

22 Experimental Methods

221 Cement Setting Time The setting time of cement withHLSAwasmeasured according toChinese BuildingMaterialsStandards JC 477-2005 with water to cement ratio (WC)040 the dosage of setting accelerator was 6 7 and 8 (bymass of cement) respectively The cement pastes were curedunder the condition of temperature 20 plusmn 2∘C and RH not lessthan 90The effect of HLSA on cement setting time at 10∘Cand 20∘Cwas investigated respectively it used Yangdong PsdotO425 Portland cement and Huaxin PsdotO 425 Portland cementand the composition mix was shown in Table 3

222 Strength Development of CementMortar Themeasure-ment of cement mortar strength development was accordingto Chinese Building Materials Standards JC 477-2005 Withstandard sand cement water ratio of 3 2 1 the additionof setting accelerator was 6 7 and 8 (by mass ofcement) respectively Cementmortar specimenswere 40mmtimes 40mmtimes 160mmprismsThe specimenswere prepared andcured in molds for 24 h under the condition of temperature20 plusmn 2∘C and RH over 90 then they were demouldedand tested for 1 d compressive strength immediately the




Yangfang PsdotO 425

106

Y10-S7 04 7Y10-S8 04 8Y20-S6 04

206

Y20-S7 04 7Y20-S8 04 8H10-S6 04

Huaxin PsdotO 425

106

H10-S7 04 7H10-S8 04 8H20-S6 04

206

H20-S7 04 7H20-S8 04 8


1198621 () = 100 times119862(1198861) minus 119862(1198871)119862(1198871)

() (1)



11986228 () = 100 times119862(11986728)119862(11986128)() (2)







2O (3)







InitialFinal

Y10-

S6

Y10-

S8

Y10-

S7

Y20-

S7

Y20-

S8

Y20-

S6

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(a) Y

InitialFinal

H20

-S6

H20

-S8

H10

-S8

H10

-S6

H10

-S7

H20

-S7

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(b) H


InitialFinal

C1

C28

28 27 26

63

4 37


7

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

Setti

ng ti

me (

min

)

30

40

50

60

70

80

90

100

(a) Y

InitialFinal

C1

C28

3 28 27

69

545


740

50

60

70

80

90

100

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

8

Setti

ng ti

me (

min

)

(b) H







Y20-S7

Blank

998771

CH998771

AFt

20 30 40102120579 (

∘)

C3SC2S

(a) 5min

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

AFm998786CH998771

AFt

C3S

C2S

998771

998771

(b) 5 h

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(c) 1 d

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(d) 28 d












Blank


Y20-S7

5min 96888 0203 311 38185 h 96884 0150 365 33061 d 96909 0108 497 324028 d 96798 0167 300 3035



Blank 1 d 49080 0154 442 412428 d 49033 0149 914 8269

Y20-S7 1 d 49135 0177 196 209828 d 48978 0189 277 3172

5min5h1d28d

200 400 600 8000Temperature (∘C)

(a) Blank

5min5h1d

28d

200 400 600 8000Temperature (∘C)

(b) Y20-S7










Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7


0

2

4

6

8

10

12

CH (

)










997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H


6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H






2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Yangfang PsdotO 425

106

Y10-S7 04 7Y10-S8 04 8Y20-S6 04

206

Y20-S7 04 7Y20-S8 04 8H10-S6 04

Huaxin PsdotO 425

106

H10-S7 04 7H10-S8 04 8H20-S6 04

206

H20-S7 04 7H20-S8 04 8


1198621 () = 100 times119862(1198861) minus 119862(1198871)119862(1198871)

() (1)



11986228 () = 100 times119862(11986728)119862(11986128)() (2)







2O (3)







InitialFinal

Y10-

S6

Y10-

S8

Y10-

S7

Y20-

S7

Y20-

S8

Y20-

S6

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(a) Y

InitialFinal

H20

-S6

H20

-S8

H10

-S8

H10

-S6

H10

-S7

H20

-S7

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(b) H


InitialFinal

C1

C28

28 27 26

63

4 37


7

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

Setti

ng ti

me (

min

)

30

40

50

60

70

80

90

100

(a) Y

InitialFinal

C1

C28

3 28 27

69

545


740

50

60

70

80

90

100

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

8

Setti

ng ti

me (

min

)

(b) H







Y20-S7

Blank

998771

CH998771

AFt

20 30 40102120579 (

∘)

C3SC2S

(a) 5min

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

AFm998786CH998771

AFt

C3S

C2S

998771

998771

(b) 5 h

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(c) 1 d

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(d) 28 d












Blank


Y20-S7

5min 96888 0203 311 38185 h 96884 0150 365 33061 d 96909 0108 497 324028 d 96798 0167 300 3035



Blank 1 d 49080 0154 442 412428 d 49033 0149 914 8269

Y20-S7 1 d 49135 0177 196 209828 d 48978 0189 277 3172

5min5h1d28d

200 400 600 8000Temperature (∘C)

(a) Blank

5min5h1d

28d

200 400 600 8000Temperature (∘C)

(b) Y20-S7










Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7


0

2

4

6

8

10

12

CH (

)










997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H


6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H






2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




InitialFinal

Y10-

S6

Y10-

S8

Y10-

S7

Y20-

S7

Y20-

S8

Y20-

S6

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(a) Y

InitialFinal

H20

-S6

H20

-S8

H10

-S8

H10

-S6

H10

-S7

H20

-S7

2

3

4

5

6

7

8

9

Setti

ng ti

me (

min

)

(b) H


InitialFinal

C1

C28

28 27 26

63

4 37


7

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

Setti

ng ti

me (

min

)

30

40

50

60

70

80

90

100

(a) Y

InitialFinal

C1

C28

3 28 27

69

545


740

50

60

70

80

90

100

Perc

enta

ge (

)

0

1

2

3

4

5

6

7

8

Setti

ng ti

me (

min

)

(b) H







Y20-S7

Blank

998771

CH998771

AFt

20 30 40102120579 (

∘)

C3SC2S

(a) 5min

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

AFm998786CH998771

AFt

C3S

C2S

998771

998771

(b) 5 h

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(c) 1 d

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(d) 28 d












Blank


Y20-S7

5min 96888 0203 311 38185 h 96884 0150 365 33061 d 96909 0108 497 324028 d 96798 0167 300 3035



Blank 1 d 49080 0154 442 412428 d 49033 0149 914 8269

Y20-S7 1 d 49135 0177 196 209828 d 48978 0189 277 3172

5min5h1d28d

200 400 600 8000Temperature (∘C)

(a) Blank

5min5h1d

28d

200 400 600 8000Temperature (∘C)

(b) Y20-S7










Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7


0

2

4

6

8

10

12

CH (

)










997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H


6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H






2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




Y20-S7

Blank

998771

CH998771

AFt

20 30 40102120579 (

∘)

C3SC2S

(a) 5min

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

AFm998786CH998771

AFt

C3S

C2S

998771

998771

(b) 5 h

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(c) 1 d

AFm998786CH998771

AFt

C3S

C2S

Blank

Y20-S7

998786

998786

20 30 40102120579 (

∘)

998771998771

(d) 28 d












Blank


Y20-S7

5min 96888 0203 311 38185 h 96884 0150 365 33061 d 96909 0108 497 324028 d 96798 0167 300 3035



Blank 1 d 49080 0154 442 412428 d 49033 0149 914 8269

Y20-S7 1 d 49135 0177 196 209828 d 48978 0189 277 3172

5min5h1d28d

200 400 600 8000Temperature (∘C)

(a) Blank

5min5h1d

28d

200 400 600 8000Temperature (∘C)

(b) Y20-S7










Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7


0

2

4

6

8

10

12

CH (

)










997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H


6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H






2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Blank


Y20-S7

5min 96888 0203 311 38185 h 96884 0150 365 33061 d 96909 0108 497 324028 d 96798 0167 300 3035



Blank 1 d 49080 0154 442 412428 d 49033 0149 914 8269

Y20-S7 1 d 49135 0177 196 209828 d 48978 0189 277 3172

5min5h1d28d

200 400 600 8000Temperature (∘C)

(a) Blank

5min5h1d

28d

200 400 600 8000Temperature (∘C)

(b) Y20-S7










Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7


0

2

4

6

8

10

12

CH (

)










997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H


6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H






2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials






Blank 1 0258 395 0051198 0051198 0106411 0050193Y20-S7 1 0235 352 0062264 0038162 0095404 0040170Blank 28 0189 297 0034180 0070370 0041217 0044233Y20-S7 28 0161 271 0023143 0073453 0028174 0037230

BlankY20-S7


0

2

4

6

8

10

12

CH (

)










997888rarr 3CSH2 + 2Al (OH)3(6)

C3A + 3CSH2 + 26H


6CH + Al2 (SO4)3 + 26H


Al (OH)3 + 3CH + 3CSH2 + 24H






2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials




2um 1um

(a) Y20-S7 5min

2um

(b) Blank 5 h

2um

(c) Y20-S7 5 h

2um

(d) Blank 1 d

2um

(e) Y20-S7 1 d

5um

(f) Blank 28 d

5um

(g) Y20-S7 28 d




4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials





4 Conclusions




Competing Interests


Acknowledgments


References




































CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



















CeramicsJournal of







Biomaterials




Journal of


Journal of





CoatingsJournal of

Advances in








MaterialsJournal of


Nano

materials



the performance and mechanism analysis of cement ...2.2.3. microstructure of hardened cement pastes....

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