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Procedia Engineering 117 ( 2015 ) 1036 – 1042
1877-7058 © 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of SPbUCEMF-2015
doi: 10.1016/j.proeng.2015.08.228
ScienceDirect
Available online at www.sciencedirect.com
International Scientific Conference Urban Civil Engineering and Municipal Facilities,
SPbUCEMF-2015
The Influence of Extra Mixing Water on the Properties of Structural
Lightweight Aggregate Concrete
Mykola Zaichenkoa,*, Serhii Lakhtarynaa, Artem Korsunb
aDonbas National Academy of Civil Engineering and Architecture, Derzhavina, 2, Makeyevka, Donetsk region, 86123, Ukraine
bSt. Petersburg State Polytechnical University, Polytechnicheskaya, 29, Saint-Petersburg, 195251, Russia
Abstract
Because of high water absorption capacity of lightweight aggregates, the workable concrete mixtures become stiff within a few
minutes of mixing. Rather, many ready mix producers will typically pre-wet the aggregate, however this procedure may
complicate the technological process. Extra water in structural lightweight aggregate concrete apart workability affects the degree
of cement hydration as well as deformation properties of concrete. So, the main objective of this research is to determine the
impact of volume of water per cubic meter of concrete needed to be supplied by LWA or by adding extra mixing water on the
properties of SLWAC – workability, slump loss, relative humidity change, autogenous shrinkage, and compressive strength.
© 2015 The Authors. Published by Elsevier Ltd.
Peer-review under responsibility of the organizing committee of SPbUCEMF-2015.
Keywords: structural lightweight aggregate concrete, extra mixing water, internal curing, workability, autogenous shrinkage.
1. Introduction
Decreasing the specific consumption of materials and reducing mass of building structures without loss of their
supporting capacity and other exploitation ability is one of the major factors of increasing the efficiency of
construction technology. Structural lightweight aggregate concrete (SLWAC) has obvious advantages of a higher
strength/weight ratio, better tensile strain capacity, a lower coefficient of thermal expansion, and superior heat and
sound insulation characteristics due to air voids in the lightweight aggregate (LWA) [1]. Unlike its normal-weight
* Corresponding author. Tel.: +380-50-478-92-60; fax:+ 380 (0626) 41-73-99
E-mail address: zaichenko_nikola@mail.ru
© 2015 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license
(http://creativecommons.org/licenses/by-nc-nd/4.0/).
Peer-review under responsibility of the organizing committee of SPbUCEMF-2015
1037
Mykola Zaichenko et al. / Procedia Engineering 117 ( 2015 ) 1036 – 1042
counterpart, SLWAC reduces dead weight loads even further because members are not only stronger, but also
lighter, lowering foundation costs for a structure as well as making the construction convenient[2, 3]. Thus, the
construction cost can be saved when applied to structures such as offshore drilling platforms, long-span bridges and
high rise buildings [4-7].
Lightweight aggregates were primarily used to reduce the weight of concrete structures. However, these
aggregates were usually saturated prior to use in concrete to ensure adequate workability, since it was recognized
that dry porous aggregates could absorb some of the mix water in fresh concrete [8]. Because of high water
absorption, the workable concrete mixtures become stiff within a few minutes of mixing. In the mixing operation the
required water and aggregate are usually premixed prior to the addition of cement. Murari Lal Gambhir reported [9]
that approximately, six liters of extra water per cubic meter of lightweight aggregate concrete is needed to enhance
the workability by 25 mm. So, it’s a standard practice to pre-soak lightweight aggregates before batching [10]. On
the other hand, in laboratory applications, soaking aggregate for 24 h prior to mixing is commonly used. In field
applications, however, soaking the aggregates is not always practical. Rather, many ready mix producers will
typically pre-wet the aggregate by placing a sprinkler on a stockpile of LWA. By sprinkling the LWA with water
and allowing time for the excess water to drain, the aggregate can reach a sufficient level of pre-wetting (a high
degree of saturation). A few producers vacuum saturate their aggregate before they are shipped, so that they arrive
with high and controlled moisture content [11].
It's necessary to mention, however, that while a majority of ready mix producers have procedures for use of pre-
wetted LWA, others have expressed concerns because it can be significantly more difficult to handle in cold weather
conditions or can lead to arching in aggregate bins [11]. Besides, because water absorbed into lightweight aggregate
is not factored into the water-cement material ratio (w/c), lightweight aggregate concrete initially contains a greater
total volume of water than a normalweight concrete mixture with the same w/c [10].
In some cases to prevent workability loss of concrete mixtures the method of delayed addition of mixing water
just before placing the concrete mix at the construction site has been adopted. At the same time, the results of
investigations of retempered concrete indicate that many of the properties of hardened concrete (strength, durability,
frost resistance, etc) are significantly affected, since retempered concrete does not perform as well as concrete which
has not been retempered [12]. When using dry expanded clay aggregate concrete slump retention can be influenced
by an excess amount of mixing water above of the original workability in relation to the target. In this case an excess
mixing water absorbed by porous aggregate does not affect the value of the effective w/c ratio and does not reduce
the strength of concrete [13].
The water stored in the lightweight aggregates is typically stored in pores that are larger than those in a hydrating
cement paste [14]. As a result the water moves from the lightweight aggregate to the surrounding cement paste
keeping the small pores saturated and playing the role of the internal curing (IC) agent [15]. There are three main
factors that influence the effectiveness of IC in concrete mixture. They are the volume of IC water provided, the
ability for water to leave the LWA when needed, and the distribution of IC water throughout the concrete matrix
[16].
The internal curing process utilizes cement more efficiently during the hydration process. Internal curing
improves the workability and reduces the cracks due to plastic, drying and thermal shrinkage. The strength of
concrete is increased as the bond between the lightweight aggregate and the hydrated cement becomes continuous
due to decrease in permeability [14]. Besides, in concretes with low w/c ratio the IC agent can mitigate the cracking
GXH WR DXWRJHQRXV VKULQNDJH VWUDLQ YDOXHV FDQ UHDFK íîí within only 24 h[8]) caused by the hydration
reactions and their accompanying chemical shrinkage [17].
The main objective of this research is to determine the impact of volume of water per cubic meter of concrete
needed to be supplied by the LWA or by adding extra mixing water on the properties of structural lightweight
aggregate concrete –workability, slump loss, relative humidity change, autogenous shrinkage, and compressive
strength.
2. Materials
Type I ordinary Portland cement (OPC 52.5) with Blaine fineness of 425 m2/kg and specific gravity of 3.15 was
used for this study. Initial and final setting times of the cement were 2 and 3 h, respectively. Silica fume (SF) was
1038 Mykola Zaichenko et al. / Procedia Engineering 117 ( 2015 ) 1036 – 1042
supplied from the Norway Elkem Microsilica (non-combustible amorphous SiO2). The specific gravity and unit
weight were 2.21 and 245 kg/m3,respectively.
The normal weight sand (NWS) used was natural river sand with a fineness modulus of 2.75, an apparent specific
gravity of 2.62, and absorption value of 1.5 % by dry mass. The LWA Leca 4–8 mm used in this study was supplied
by Denmark LECA Company. The bulk density, dry particle density and 24-h water absorption (Fig. 1) values of the
lightweight aggregate were found to be 385 kg/m3, 710 kg/m3and 28.6 %, respectively.
Superplasticizer (SP) Sika Viscocrete-2300 HE and tap water (W) were used in this investigation.
3. Mixture proportioning
A total of four formulations of mixtures were prepared. The formulation No. 1 is the mortar with the binding
(OPC+SF)/aggregate (NWS) ratio of 1.64 and w/c ratio of 0.25. In the formulations No. 2, 3, 4 the part of mortar
volume is replaced by equivalent portion of LWA (40 %): vacuum saturated (2), oven-dry (4) and oven-dry with
surface treatment by hydrophobic spray (3).
The volume of water per cubic meter of concrete needed to be supplied by the LWA for internal curing (or extra
water) can be calculated by Eq. (1), proposed by Bentz and Snyder [18]:
ȡ
ĮCSC
concretem/waterm(V
maxf
wat
,(1)
where Cf(kg/m3) is the cement content of the mixture, CS (0.06 kg of water per 1 kg of cement) is the chemical
shrinkage of the cement, Dma x (unitless) is the expected maximum degree of hydration (0–1), Uis the density of
water (1000 kg/m3). For concretes with w/c ratios below 0.40 (typical SLWAC or HPC), complete hydration cannot
be achieved and the maximum degree of hydration, Dmax can be estimated as (w/c)/0.40 [18].
In accordance with Eq. (1), the volume of extra water in formulation 4 was found to be 0.025 m3.
A complete list of mixture proportions used in this study is found in Table 1.
Table 1. The mixtures proportions.
No Formulation OPC [kg/m3]SF [kg/m3]NWS [kg/m3]W[l/m3]LWA [kg/m3]SP [l/m3]Air [%]
1LWA 0 % 1113 167 779 250 -13.4 4.5
2LWA 40 %
(vacuum saturated)
667 100 467 159 300 8.0 3.1
3LWA 40 % (dry, spray) 667 100 467 159 300 8.0 3.1
4LWA 40 %
(dry+15 % extra water)
667 100 467 159+25 300 8.0 3.1
4. Experimental methods
4.1. Workability measurements
Immediately after mixing and every 20 minutes after mixing, the concrete mixtures were subjected to rheological
(slump flow) tests with the help of the Abrams cone. The spread diameter was measured on a horizontal plate once
the flow had stopped. It corresponded to the average of two diameters.
4.2. Determination of compressive strength
Nine 100 mm u200 mm cylinders were cast for each mixture. After 24 h the samples were demolded and moist
stored in container at the temperature of +30qC. The compressive strength of the three cylinders were measured at 1
d, 7 d, and 14 d in accordance to ASTM C39-09.
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Mykola Zaichenko et al. / Procedia Engineering 117 ( 2015 ) 1036 – 1042
4.3. Autogenous RH measurements
The fresh paste was cast into the measuring chamber of two Rotronic hygroscopic DT stations (Fig. 2a) equipped
with WA-14TH and WA-40TH measuring cells (Fig. 2b). The RH stations were placed in a thermostatically
controlled room at 20 ± 0.1qC. The development of the RH in the samples and the temperature were continuously
measured for a period of about 1 week after mixing. Before and after the measurements, calibration of the stations
was carried out with four saturated salt solutions in the range of 75-100 % RH. This procedure results into a
measuring accuracy of about ± 1 % RH [17].
4.4. Autogenous deformation measurements
The cement paste was cast under vibration into tight plastic moulds, which were corrugated to minimize restraint
on the paste. The length of the samples was approximately 350 mm. The specimens were placed in a dilatometer
(Fig. 3), which was immersed into a temperature-controlled glycol bath at 20 ± 0.1qC. Two samples were tested
simultaneously in the dilatometer, with a measuring accuracy of ±5 microstrain. Continuous linear measurements
were started directly after casting [17].
Fig. 1. 24-h water absorption of LWA Fig. 2a. Rotronic hygroscopic DT station
Fig. 2b. WA-40TH measuring cell Fig. 3. Dilatometer for autogenous deformation measurements
1040 Mykola Zaichenko et al. / Procedia Engineering 117 ( 2015 ) 1036 – 1042
5. Results obtained
5.1. Slump loss of concrete mixtures
Slump loss measurement was investigated during 60 minutes after mixing. As can be seen from Fig. 4 all
concrete mixtures had slump loss during 60 minutes. The formulation 2 with vacuum saturated LWA had minimal
value of slump loss –about 7 %. The mixing water did not absorbed by porous aggregate and small value of slump
loss is due most likely to adsorption of superplasticizer onto the surface of hydration products of Portland cement.
The extra volume of mixing water (15 %–formulation No. 4) provided an initial slump flow of concrete mixture,
similar to the formulation No. 2. However, slump loss within 60 min reached 24 %. This testifies to the sufficient
intensity of the absorption rate of moisture by dry porous aggregates. Theoretically, according to the24-h water
absorption curve (Fig. 1), absorption quantity within the first three hours (corresponding to the setting time of the
cement paste) is about 23 %. So, 300 kg per cubic meter of dry LWA can absorb to 69 liters of moisture. That’s why
the volume of 0.025 m3of extra mixing water needed for internal curing of concrete can not compensate slump loss
of concrete mixture. However, when the LWA is placed in dry form in the paste mixture, some pores in the LWA
could become blocked by cement and silica fume particles during the absorption process. Also, the viscosity and
surface tension of the pore solution will be different (higher) from those of water. This will likely produce a
reduction in the rate at which the LWA absorbs the fluid.
Fig. 4. Slump loss of concrete mixtures
Regarding the composition of the concrete mixture No. 3 (hydrophobized LWA), slump loss of 17 % indicates
that hydrophobic film on the surface of the grain does not completely block the ingress of moisture into the core.
5.2. Autogenous RH and deformation measurements
As can be seen from Fig. 5 a significant rise in the value of the autogenous deformations occurred in the period of
mortar hardening between 5–24 h, when the shrinkage was 2200 microstrain. This time period corresponds
accordingly to the sharp drop in RH value from 100 % to 93 % (Fig. 6). The following part of autogenous internal
RH curve (period between 2 and 5 days) corresponds to slow rate of RH change. Finally, at the age of 14 days the
drop of RH magnitude reached the value of 80 %. Together with falling the value of RH there is an increase of
autogenous shrinkage up to 2600 microstrain. So, most of the autogenous shrinkage of mortar caused by internal
self-desiccation developed within the first week of hydration.This observation, therefore, suggests that the
prevention of excessive self-desiccation and autogenous shrinkage cracking in SLWA structures should involve
techniques that are effective for at least one week after mixing and casting.
It can be observed from Fig. 7 that all LWA concrete specimens first experienced light expansion resulting in
compressive stresses during the first 48 h, followed by shrinkage and tensile stresses developing in the specimens of
formulation 3 and formulation 4. On the other hand, the specimen of formulation 2, which had 40 % of vacuum
200
250
300
350
020 40 60
Slump flow, mm
Time (min)
2 (40% LWA Vacuum Saturated)
3 (40 % LWA Spray )
4 ( 40% LW A 1 5% E xtra w ate r)
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Mykola Zaichenko et al. / Procedia Engineering 117 ( 2015 ) 1036 – 1042
saturated LWA up to 14 days experienced expansion. It should be noted that during this period concrete mixture
reserved the value of RH from 97 to 96.6 % (Fig. 8). While the mechanisms of internal curing contributing to a
reduction in autogenous shrinkage are well known, the mechanisms leading to an early-age expansion are not well
understood. The expansion was most likely due to the crystallization pressure caused by the ettringite formation
and/or swelling of the gel hydration products, which are generally considered as a principal cause of early-age
expansion [19]. Thus, autogenous shrinkage was completely prevented in the structural lightweight aggregate
concrete with vacuum saturated porous aggregate.
In the case of dry aggregate (formulations 3,4) the autogenous shrinkage magnitude reached the value of
íîí DQGíîí microstrain, accordingly. The monotonically increasing autogenous shrinkage within the
period from 3 to 14 days accompanied with decreasing the value of RH from 93–95 to 82–85 % (Fig. 8). The
formulation 3 (dry hydrophobized LWA) had no any additional reservoir to keep internal curing water and,
accordingly, to prevent autogenous shrinkage. When extra mixing water, the amount of which was calculated on the
basis of condition to ensure the internal curing, was added to the concrete mixture with the dry porous aggregate, the
development of autogenous shrinkage was probably due to the limitation of water absorption by LWA in a viscous
FHPHQW SDVWH HQYLURQPHQW 2Q WKH RWKHU KDQG WKH YDOXH RI DXWRJHQRXV VKULQNDJH íîí microstrain is not
critical for early-age cracking, corresponded to the time with the highest net shrinkage strain to tensile strength ratio
(12–36 hours) [8].
Fig. 5. Autogenous deformation measured on mortar after setting Fig. 6. Autogenous internal RH measured on mortar
Fig. 7. Autogenous deformation measured on concrete mixtures after
setting Fig. 8. Autogenous internal RH measured on concrete mixtures
-2700
-2200
-1700
-1200
-700
-200
012345678910 11 12 13 14
Autogenous Strain [um/m]
Age of Specimen (Days)
1 (0% LWA)
75
80
85
90
95
100
012345678910 11 12 13 14
RH, %
Age of Specimen (Days)
1 (0%LWA)
-200
-150
-100
-50
0
50
100
150
200
012345678910 11 12 13 14
Autogenous Strain [um/m]
Age of Specimen (Days)
2 (40% LWA Vacuum
saturated)
75
80
85
90
95
100
012345678910 11 12 13 14
RH, %
Age of Specimen (Days)
2 (40% LWA Vacuum
saturated)
3 (40% LWA Spray)
1042 Mykola Zaichenko et al. / Procedia Engineering 117 ( 2015 ) 1036 – 1042
5.3. Compressive strength
Partial replacement of mortar (formulation 1) with porous aggregates significantly reduced the compressive
strength of concrete. Thus the positive impact on the strength development had pre-wetting (vacuum saturation) of
LWA (formulation 2). Extra mixing water in the formulation 4 enhanced early compressive strength, but at a later
date of curing SLWA No. 4 had slightly lower strength compared to other formulations.
6. Summary
Vacuum saturated, oven-dry, and oven-dry with surface hydrophobization LWAs were tested to determine their
influence on the workability behaviors as well as internal curing performance of LWAC. When extra mixing water
used in concrete with an oven-dry state LWA mixture is unable to prevent slump loss during 60 min after mixing.
The majority of the water absorbed by the LWA (vacuum saturated) is then returned as internal curing water to the
cement paste after setting to enhance the properties of concrete (increase in compressive strength and prevention of
autogenous shrinkage), while concrete with oven-dry aggregate and extra water did not perform as well as the first
one. The main problem is a complexity to determine an actual water absorption of LWA in viscous cement paste
with ultra fine mineral fillers. So, it's necessary to elaborate the reliable technique to calculate the amount of water
that will be available for internal curing.
References
[1] Topcu, I.B. Semi-lightweight concretes produced by volcanic slags (1997) Cement and Concrete Research, 27, pp. 15–21.
[2] High-Strength Concrete (1994) Portland Cement Association: Concrete Technology Today, 15 (1), pp. 1–4.
[3] Choi, Y.W., Kim, Y.J., Shin, H.C., Moon, H.Y. An experimental research on the fluidity and mechanical properties of high-strength
lightweight self-compacting concrete (2006) Cement and Concrete Research, 36, pp. 1595–1602.
[4] Holland, R.B., Kahn, F.L. High strength lightweight concrete properties of the I-85 Ramp over State Route 34 (2010) HPC Bridge Views,
61, pp. 1–10.
[5] Liles, P., Holland, R.B. High strength lightweight concrete for use in precast, prestressed concrete bridge girders in Georgia (2010) HPC
Bridge Views, 61, pp. 1–10.
[6] "State-of-the-Art Report on Offshore Concrete Structures for the Arctic". Reported by ACI Committee 357 -ACI 357.1R-91 (Reapproved
1997) American Concrete Institute, Detroit, Michigan.
[7] Owens, P.L. Structural lightweight aggregate concrete –the future? (1999) Concrete, 33 (10), pp. 45–47.
[8] Cusson, D., Hoogeveen, T. Internal curing of high-performance concrete with pre-soaked fine lightweight aggregate for prevention of
autogenous shrinkage cracking (2008) Cement and Concrete Research, 38, pp. 757–765.
[9] Murari Lal Gambhir. Concrete Technology: Theory and Practice: Fifth Edition (2013) Concrete Technology: Theory and Practice: Fifth
Edition, 763 p.
[10] Craig, P., Wolfe, B. Another look at the drying of lightweight concrete: A comparison of drying times for normalweight and lightweight
floors (2012) Concrete international, January 2012, pp. 53–56.
[11] Golias, M., Castro, J., Weiss, J. The influence of the initial moisture content of lightweight aggregate on internal curing (2012) Construction
and Building Materials, 35, pp. 52–62.
[12] Collepardi, M., Valente, M. Recent developments in superplasticizers (2006) Proc. of the 8-th Intern. Conf. on Superplasticizers and Other
Chemical Admixtures in Concrete, pp. 1–14.
[13] Bazhenov, Y.M. Tekhnologia betona [Concrete technology]: Fourth Edition (2007) Tekhnologia betona [Concrete Technology]: Fourth
Edition, 528 p.
[14] Dayalan, J., Buellah, M. Internal curing of concrete using prewetted light weight aggregates (2014), International Journal of Innovative
Research in Science, Engineering and Technology, 3 (3), pp. 10554–10560.
[15] Kovler, K., Jensen, O. Novel techniques for concrete curing (2005) Concrete International, 27 (9), pp. 39–42.
[16] Henkensiefken, R., Bentz, D., Nantung, T., Weiss, J. Volume change and cracking in internally cured mixtures made with saturated
lightweight aggregate under sealed and unsealed conditions (2009) Cement and Concrete Composites, 31, pp. 427–437.
[17] Lura, P., Jensen, O.M., van Breugel, K. Autogenous shrinkage in high-performance cement paste: An evaluation of basic mechanisms
(2003) Cement and Concrete Research, 33, pp. 223–232.
[18] Bentz, D.P., Snyder, K.A. Protected paste volume in concrete. Extension to internal curing using saturated lightweight fine aggregate (1999)
Cement and Concrete Research, 29, pp. 1863–1867.
[19] Sahmaran, M., Lachemi, M., Hossain, K.M.A., Li, V.C. Internal curing of engineered cementitious composites for prevention of early age
autogenous shrinkage cracking (2009) Cement and Concrete Research, 39, pp. 893–901.
