Concrete with clinker‐efficient cements ‐ Robustness to variations in water content and temperature

The use of multi‐component cements (CEM II‐CEM VI), which contain main constituents other than Portland cement clinker in significant quantities, can significantly help to reduce the CO2 footprint of the cement or concrete industry. Clinker‐efficient cements (CEM II/C‐M) have been standardized in the current version of DIN EN 197‐5. In a systematic experimental program, the influence of water content variations and temperature on the robustness of concrete with clinker‐efficient cements with high contents of granulated blast furnace slag or fly ash and limestone (CEM II/C‐M (S‐LL) and CEM II/C‐M (V‐LL)) was studied. As a reference, concretes representative for construction elements used indoor (XC1) or in protected outdoor environment (XC3) with standard Portland composite cement (CEM II/A‐M) and blast furnace slag cement (CEM III/A) were investigated. The influence of variations in water content and temperature on fresh (rheological properties, bleeding) and mechanical concrete properties (compressive strength, elastic modulus) were investigated. The results obtained show similar performance and robustness of such concretes with clinker‐efficient cements compared to the reference concretes.


Introduction
The production of concrete and especially its constituent cement is associated with significant CO2 emissions.Cement production alone is responsible for more than 6.7 % of the world's total anthropogenic CO2 footprint [1].According to the world climate targets agreed at the UN climate conferences, a significant reduction in emissions from cement and concrete production is imperative [2].
The CO2 footprint of the cement production can be mitigated by various means.However, the individual options differ strongly in the technical measures, the normative requirements and in the required investments.With regard to the material side, there are mainly two possible pathways:  Replacing Portland Cement clinker: Production and use of multi-component cements (CEM II-CEM VI) containing significant quantities of main constituents other than Portland cement clinker [3][4][5]. New clinker formulations: Modification of the production process and development of new clinker formulations e.g. based on calcium sulfoaluminate [6] or belite [7].
In the production of ready-mix concrete in Germany already today Portland composite cements based on granulated blast furnace slag (S), limestone powder (LL) or fly ash (V) dominate the market.These cements have a lower environmental footprint than pure Portland cement [8,9].However, e. g. more than 80 % of the blast furnace slag that is available worldwide, is already used as cement or concrete additive [10], thus significantly limiting the possibilities for a substantial increase in clinker replacement by slag.A promising option are clinker-efficient cements using moderate amounts of granulated blast furnace slag in combination with limestone [3].These clinker-efficient cements (CEM II/C-M) are included in DIN EN 197-5 [11].CEM II/C-M-cements contain at least 50 wt.%Portland cement clinker and 36-50 wt.% of other constituents, such as combinations of blast furnace slag and limestone or fly ash and limestone (amount of LL is limited to 6-20 wt.%).
There are various studies in the literature on the performance of concretes with clinker-efficient CEM II/C-Mcements in terms of mechanical properties and durability [12][13][14][15][16]. Palm et al. [12] analysed the performance and the environmental impact of concretes made with clinkerefficient cements with high contents of granulated blast furnace slag and limestone.They showed that cements with a Portland cement clinker content of approx.50 wt.%

Abstract
The use of multi-component cements (CEM II-CEM VI), which contain main constituents other than Portland cement clinker in significant quantities, can significantly help to reduce the CO2 footprint of the cement or concrete industry.Clinker-efficient cements (CEM II/C-M) have been standardized in the current version of  In a systematic experimental program, the influence of water content variations and temperature on the robustness of concrete with clinker-efficient cements with high contents of granulated blast furnace slag or fly ash and limestone (CEM II/C-M (S-LL) and CEM II/C-M (V-LL)) was studied.As a reference, concretes representative for construction elements used indoor (XC1) or in protected outdoor environment (XC3) with standard Portland composite cement (CEM II/A-M) and blast furnace slag cement (CEM III/A) were investigated.The influence of variations in water content and temperature on fresh (rheological properties, bleeding) and mechanical concrete properties (compressive strength, elastic modulus) were investigated.The results obtained show similar performance and robustness of such concretes with clinker-efficient cements compared to the reference concretes.
using granulated blast furnace slag and a limestone content of 20 wt.% as the main constituent are basically suitable for the production of structural concretes.The fresh and hardened concrete properties were comparable to concretes already used in practice, with the exception of freeze-thaw resistance [12].Kròl et al. [14] showed that the properties of concretes with CEM II/C-M-cements result from the properties of the main constituents of the cement and the synergistic interaction of the composition.Thus, higher compressive strengths were reached when granulated blast furnace slag (S) was combined with limestone (LL) rather than fly ash (V) with limestone (LL).This is due to the higher activity of blast furnace slag compared to fly ash [14].Müller et al. [13] showed that the workability of concretes with clinker-efficient cements is comparable to concretes with established cements (all concretes without superplasticizer).However, to ensure durability, a reduced w/c-ratio is required for concretes with clinkerefficient cements [14].In this case, superplasticizer can ensure workability.Neufert et al. [16] investigated the robustness of concretes with ternary blended cements containing blast furnace slag and limestone to variations in water content and temperature.The results show that the compressive strength of the concretes with clinker-efficient cements is more sensitive to changes in water content than concretes with CEM III/A.The same applies to the carbonation resistance [16].Further systematic investigations on the robustness of concretes with clinker-efficient cements against practice relevant variations (e.g.water content or temperature) are currently missing in the literature.
For construction practice, robustness with regard to variations in water content is of particular importance.For example, the water content might vary due to an inaccurate determination of the moisture content of the fine aggregates.Billberg and Westerholm [17] e.g.showed that varying the water content has a significantly greater effect on the rheological properties of concrete than varying the content of fine particles or temperature.
The aim of this study was to analyse the robustness to systematic water content variations of concretes made with clinker-efficient cements containing high contents of granulated blast furnace slag and limestone (CEM II/C-M (S-LL)) or fly ash and limestone (CEM II/C-M (V-LL)), respectively.The influence of variations in water content on the fresh properties and mechanical behaviour were investigated.As reference, concretes with standard Portland composite cement (CEM II/A-M) and blast furnace slag cement (CEM III/A) were investigated.Two water content variations (± 1.5 wt.% and 2.5 wt.% of the mass of sand) and three different temperatures (10 °C, 20 °C and 30 °C) were studied.The investigated variations were selected as representative of possible deviations in practical concrete production, taking into account the permissible tolerances according to [18].

Materials and concretes
In this study, concretes with a w/c-ratio of 0.65, a paste content of 275 l/m³ and a maximum grain size of 16 mm with various cement types were prepared (cf.Table 1).In practice, this composition is representative for construction elements used indoors (XC1) or in protected outdoor environments (XC3).For all mixtures cements according to DIN EN 197-1 [19] or  were used.On the one hand, Portland composite cements with various types and amounts of additives (CEM II/A-M (V-LL), CEM II/C-M (S-LL), CEM II/C-M (V-LL)) as well as a blast furnace slag cement (CEM III/A) were investigated.
Here, CEM II/A-M (V-LL) and CEM III/A are representative of German construction practice [9] and serve as reference in this study.Table 2 summarizes the main physical properties and Figure 1 shows the different grading curves of the cements and aggregates.For all aggregates Weser river sand and gravel were employed.The grading curve of the aggregates was chosen to be AB16 (DIN 1045-2 [20]), consisting of the fractions 0/2, 2/8 and 8/16 (grading curves see Fig. 1).All Aggregates were used in dry condition.
Figure 1 Grading curves of the raw materials (cements and aggregate) As described above, all reference concretes were prepared with a constant paste content of 275 l/m³ and the consistency was adjusted to a constant spread flow diameter of 48 ± 2 cm (DIN EN 12350-5 [21]) at the age of 5 min after water addition by adding a polycarboxylate-based superplasticizer.The dosage of superplasticizer varied depending on the cement type.All concrete mixtures were prepared in batches of 50 l and mixed with a rotating pan mixer (Zyklos, Pemat Mischtechnik GmbH) with a maximum output of 75 l of non-compacted concrete.The mixing sequence is presented in Table 3.Each reference concrete (see Tab. 1) was modified using two water content variations (+1.5 wt.%Sand and +2.5 wt.%Sand), however without adapting the mix design.This resulted in a variation of water content of 11 kg/m³ and 18 kg/m³, respectively.The amounts of raw materials other than water were not changed because the variation itself simulates unknown deviations from the target value.In a first step, all concretes were prepared with a fresh concrete temperature of 20 ± 2 °C.Selected concretes were also prepared with a fresh concrete temperature of 10 ± 2 °C and 30 ± 2°C.For this purpose, the raw materials (aggregates, cement and water) were stored at the indicated temperature for 24 hours.All, the mixing of the concrete, the testing of the fresh concrete and the preparation of test specimens were carried out at the appropriate temperature.

Test methods
In a first step after mixing, the consistency was tested 10 minutes after initial water-cement contact using the flow table test (DIN EN 12350-5 [21]).Additionally, the air void content according to DIN EN 12350-7 [22] and the fresh concrete density according to DIN EN 12350-6 [23] were determined.The rheological measurements were performed with an eBT-V Rheometer (Schleibinger Geräte Teubert u.Greim GmbH).Details about the measuring setup can be found in [24].The Bingham parameters (yield stress (0) and plastic viscosity (μ)) were derived according to the Reiner-Riwlin equation [25,26].
The bleeding test was performed according to the procedure described in [27] ('bucket' test).The test vessel was filled in two layers and compacted on the vibrating table.
In contrast to the procedure described in [27], a constant compaction energy of 4500 U/min for 15 s was applied regardless the flowability.At specific time intervals, the water on the surface of the fresh concrete was collected with a pipette.After weighing, the water was returned to the concrete.The first measurement was made 30 min after the end of mixing and was repeated in intervals of 30 min.The measurement was stopped as soon as the maximum amount of separated water was reached.Based on the measurement of the density of the fresh concrete and the sample mass, the quantity of water separated per m³ could be calculated.
The compressive strength was determined according to DIN EN 12390-3 [28] on specimens 100 mm x 100 mm x 100 mm after 2 d, 7 d and 28 d.The specimens were stored in the formwork for 24 hours at the ambient temperature and then stored under water until testing.The elastic modulus was determined according to DIN EN 12390-13 [29] on cylindrical specimens 150 mm x 300 mm after 28 d.The storage was identical to that of the specimens for compressive strength testing.

Experimental results
As pointed out, in the presented investigations the effect of uncertainties in the water content of the sand are simulated.First, the influence of water content variations at 20 °C on the fresh and hardened concrete properties will be shown.Then the combined effect of water content variations and temperature (10 °C and 30 °C) are discussed.

Fresh concrete properties
As outlined in Section 2, the consistency, the air void content and fresh concrete density, the rheological properties (yield stress (0) and plastic viscosity (μ)) and the bleeding behaviour were determined.The fresh concrete density ranged from 2330 kg/m³ to 2380 kg/m³ and the air void content from 0.6 to 1.4 Vol.-%.

Consistency
Figure 2 shows the results of the flow table test for all concretes investigated with different water contents depending on the investigated variation and the type of cement at 20 °C.The initial consistency determined 5 min after water addition of all concretes regardless of the cement type was adjusted to 48 ± 2 cm by adapting the superplasticizer (SP) content.The concretes with the ternary blended cements (CEM II/C-M (V-LL) and CEM II/C-M (S-LL)) required slightly higher superplasticizer dosages in order to achieve the target consistency compared to the concretes with CEM II/A-M (V-LL) and CEM III/A.For CEM II/C-M (V-LL) a dosage of 1.16 wt.%Cement and for CEM III/A or CEM II/A-M (V-LL) a dosage of 0.65 wt.%Cement was required (cf. Figure 2).As expected, in all cases the consistency is clearly increased by the addition of water.However, the concretes with ternary blended cements show a greater increase in consistency compared to CEM II/A-M and CEM III/A concretes.At a water dosage variation of +2.5 wt.%Sand, the consistency increases from 48.0 cm to 64.5 cm using CEM II/C-M (V-LL) and to 63 cm using CEM/C-M (S-LL), respectively.In contrast, a consistency of about 57.0 cm is achieved with CEM III/A and CEM II/A-M (V-LL) for the same water dosage variation.

Rheological properties
Figure 3 summarizes the rheological response (yield stress and plastic viscosity) to variations in the water content.The rheological properties of concrete or mortar are highly influenced by the rheology of the cement paste contained in the concrete as well as by the aggregates [30].Therefore, two categories can be divided, which are responsible for the specific rheology and robustness of concrete: factors affecting the fluid phase (cement paste) and factors affecting the solid phase (sand and coarse aggregate) [31].In this study, the same type and amount of aggregate was used for all concretes investigated, so changes in particle size distribution and morphology of the solid phase can be ruled out in explaining the observed effects.
Only the solid phase of the cement paste was varied.To describe the rheological properties, it is common to analyse the relationship between the rheological parameters and the relative solids volume fraction (Φi/Φmax) [31].The amount of cement in the mixture is considered with the solids volume fraction or phase content (Φi).The properties of the cement particles are considered by introducting the maximum packing density (Φmax), which depends on their fineness and morphology.Relative solids volume fraction (Φi/Φmax) is traditionally used in models to describe the viscosity of particle suspensions, where an increase in particle concentration leads to an increase in viscosity [32].The same applies for the yield stress, since flow can only start after the interpaticular friction has been exceeded [33].The yield stress of a suspension is determined by the friction between the particles, which in turn depends on the relative volume fraction of the solids (Φi/Φmax).For the reference concretes investigated, the relative solids fraction Φi/Φmax is mainly influenced by the water demand of the individual cement types (assuming a similar density of the cements (cf.Table 2)).Results of different investigations in the literature show the robustness to water content variations depends on the amount of free water [34][35][36].Accordingly, the robustness to water content variations increases with a higher w/cratio and a lower water demand of the binder.Transferred to the investigations presented in this study, the cements with the highest water demand show the lowest robustness against water content variations.The CEM II/A-M (V-LL) and CEM III/A have a comparatively low water demand of 0,448 and 0,458.In contrast, the water demands of the ternary blended cements are higher and reach values up to 0,471 (CEM II/C-M (S-LL)) and 0,475 (CEM II/C-M (V-LL)), respectively.The changes in the yield stress due to the increased water content are greater for the concretes with the ternary blended cements.

Bleeding
The bleeding test was performed according to the procedure (bucket method) described in [27].Only the maximum amount of water separated (max.bleeding water) is used for the presented evaluation, regardless of time and progression.Figure 4 shows the values of the maximum bleed-water for all concretes tested at 20 °C.In the reference scenario (i.e. at design water content with w/c = 0.65) clear differences between the different cements can be observed, with CEM III/A showing the most pronounced bleeding tendency with 10.3 kg/m³ and the concrete with CEM II/C-M (V-LL) showing the lowest with 0.6 kg/m³.A clear connection to physical cement properties such as the fineness (cf.Table 2) could not be established.Results from Alonso and Schäffel [37] show comparable tendencies.In the investigations concretes CEM II/A-LL-cements showing a lower tendency to bleeding compared to blast furnace cements (CEM III/A).This indicates that the limestone powder in the ternary blended cements has a positive reducing effect on the bleeding tendency.
The amount of bleeding depends on the water content, so that for the same type of cement an increase in water separation can be observed with increasing w/c-ratio.The concretes with CEM III/A and CEM II/A-M (V-LL) react pronouncedly to a water overdosage of 1.5 wt.%Sand.When using CEM II/C-M (S-LL), a significantly lower increase in the maximum bleed-water amount with increasing water content is observed.Regardless of water dosage variation, the concretes with CEM II/C-M (V-LL) show a very low tendency to bleeding.

3.2
Hardened concrete properties

Compressive strength
The compressive strengths at 2 d, 7 d and 28 d for all concretes investigated at 20 °C are presented in Figure 5.As expected, a decrease in compressive strength is observed for all concretes due to the variations in water content with increasing w/c ratio.The decrease in compressive strength depends on both the type of cement and its age.Concretes made with CEM II/C-M (V-LL) and CEM II/C-M (S-LL) exhibit a similar compressive strength at the early age (2 d and 7 d) as the reference concrete with CEM III/A.This is explained by the equal Portland cement clinker content (≈ 50 wt.%) in all these cements.The concrete with CEM II/A-M (V-LL) shows significantly higher values at this age, mainly due to the higher content of Portland cement clinker (≈ 80-85 wt.%).The decrease in compressive strength due to the performed water content variations is comparable for all cements at the early age.At the age of 28 days, a clear influence of the cement type on the compressive strength is observed.The concretes with CEM II/A-M (V-LL) and CEM III/A show comparable strength values (46.9 MPa and 48.6 MPa) for the reference composition (w/c = 0.65).In contrast, the values for the concretes with the ternary blended cements are significantly lower at 38.0 MPa (V-LL) and 36.5 MPa (S-LL).The influence of water dosage variations is on a comparable level for the concretes with highly blended cements (CEM III and CEM II/C-M).The concrete with CEM II/A-M (V-LL) reacts slightly more sensitive to variations in water dosage, therefore a stronger decrease in compressive strength with increasing w/c-ratio is observed.

Elastic modulus
The elastic modulus was determined according to DIN EN 12390-13 [29] on cylindrical specimens 150 mm x 300 mm after 28 d.The results for all concretes investigated are shown in Figure 6 as a function of mean compressive strength (fcm or fc,cyl).The compressive strength values were determined on the same specimens used for the elastic modulus testing.For comparison, Figure 6 shows the prediction of the elastic modulus according to fib Model Code 2010 [38] and DIN 1045-1 [39].It can clearly seen that the predictions of DIN 1045-1 are more conservative than the recommendations of fib Model Code 2010.All values of the elastic modulus are in a comparable range between 23.5 GPa to 26.7 GPa regardless of the cement type or water content.Surprisingly, no significant influence of cement type or water dosage variation on the elastic modulus of the concretes could be detected, although there are differences in compressive strength values due to these parameters.It should be noted that the values of elastic modulus were determined after 28 days and thus at a relatively early stage of hydration, considering the clinker content.Both the compressive strength and the modulus of elasticity of concrete increase with age (> 28 d), but at a decreasing rate.The rate of increase of the elastic modulus is less than that of the compressive strength at higher ages [38,40].Especially for concrete with CEM III/A, a significant increase in both compressive strength and elasticity modulus can be expected beyond 28 days due to the blast furnace slag [41].fib Model Code 2010 suggests a simple calculation formula for the development of elastic modulus with age, combining the elastic modulus after 28 days (Eci(28d)) with an aging coefficient (βE(t)) in a product approach [38].For slow hardening cements, an increase of Eci(365d)/Eci(28d) ≈ 1.2 can be assumed [40].Ternary blended cements (CEM II/C-M) show a slightly reduced potential of subsequent hardening beyond 28 days compared to blast furnace cements (CEM III/A) due to the lower amount of granulated blast furnace slag [14].However, it is more pronounced compared to standard Portland composite cements (CEM II/A) with max.20 wt.% secondary cementitious materials.Accordingly, an increase in the elastic modulus after 28 days can also be assumed for concretes with clinker-efficient cements (CEM II/C-M).

Influence of fresh concrete temperature and ambient temperature
In addition to the investigations already presented at 20 °C, selected concretes were additionally prepared with a fresh concrete temperature of 10 ± 2 °C and 30 ± 2 °C, respectively.For this purpose, the raw materials (aggregates, cement and water) were stored at the indicated temperature for 24 hours.The mixing of the concrete, the testing of the fresh concrete and the preparation of test specimens were carried out at the appropriate ambient temperature.The specimens for hardened concrete properties were stored for 48 hours at 10 °C in the formwork and then in water.At 30 °C they were demoulded after 24 hours and then stored under water.
The target consistency (48 ± 2 cm) could be achieved for all concretes regardless of the cement type and temperature.The dosage of superplasticizer was slightly adjusted to compensate for temperature related effects.As expected, the early strength (2 d) is lower at low temperature (10 °C) and higher at high temperature (30 °C) than at the reference temperature of 20 °C.After 28 days, a slight increase in the compressive strength of the concretes at 10 °C compared to the reference at 20 °C is for the highly blended cements (CEM III/A and CEM II/C-M).Maximum bleeding water performed according to the procedure (bucket method) described in [27] as a function of temperature An influence of water dosage variation (+1.5 and +2.5 wt.%Sand) on the compressive strength in combination with temperature could not be detected.As the w/c ratio increases, the compressive strength decreases regardless of temperature and cement type.In addition, no effect of lower temperature (10 °C) on the elastic modulus (testing after 28 d) could be detected (cf. Figure 6).
The fresh concrete and ambient temperature in particular influences the bleeding of the concrete.Figure 7 shows the maximum bleed-water as a function of temperature for concrete with different cement types.At 30 °C, a low maximum bleeding amount of less than 5,0 kg/m³ can be observed for all concretes regardless of cement type and water content (0.0 and +2.5 wt.%Sand).However, at 10 °C, there is a clear dependence on the cement type.The concrete with CEM III/A with 34.3 kg/m³ shows the most pronounced and the concrete with CEM II/C-M (V-LL) with 3.0 kg/m³ the least pronounced bleeding at 10 °C.The concretes with CEM II/A-M (V-LL) and CEM II/C-M (S-LL) show similar values of bleed-water (≈ 10.0 kg/m³) at 10 °C.These concretes react comparably to temperature variations with regard to bleeding.

Conclusion
In this study, the robustness of concrete with clinker-efficient cements and high contents of granulated blastfurnace slag or fly ash and limestone (CEM II/C-M (S-LL) and CEM II/C-M (V-LL)) to systematic water content and temperature variations was investigated.The influence of these parameters on fresh and mechanical concrete properties were investigated.In construction practice, robustness to variations in water content is of particular importance.For example, the water content may vary due to inaccurate determination of moisture content of the fine aggregate fractions.In addition, the influence of temperature on the strength development of cements with low clinker content is becoming increasingly important.The tests were carried out on concretes (C20/25) that are commonly used in practice for construction elements used indoor (XC1) or in protected outdoor environment (XC3).The main conclusions, which can be drawn for the present study are as follows:  The concretes containing ternary blended cements (CEM II/C-M (V-LL) and CEM II/C-M (S-LL)) require slightly higher superplasticizer dosages to achieve a comparable consistency (48 ± 2 cm) than the concretes with CEM II/A-M (V-LL) or CEM III/A.In addition, the concretes with ternary blended cements react more sensitively to variations in water content in terms of consistency or rheological properties such as yield stress. The type of cement significantly affects the bleeding behaviour of the investigated concretes and their sensitivity to water dosage variations.The sensitivity however cannot be derived as a function of clinker content or number of constituents.Especially when using CEM II/C-M (V-LL), both a very low bleeding tendency and a high robustness to variations in water content could be observed. A decrease in compressive strength with increasing w/c-ratio or water content can be observed in all concretes.This is comparable for all cements at an early age (2d and 7 d). At the age of 28 days, a clear influence of the cement type on the compressive strength can be observed for the reference concretes (w/c = 0.65).The concretes with CEM II/A-M (V-LL) and CEM III/A show comparable strength values.In contrast, the strength values for the concretes with the ternary blended cements (CEM II/C-M (S-LL) and (V-LL)) are significantly lower. The influence of water dosage variations on concrete with CEM III/A is on a comparable level to that of concretes with highly blended cements (CEM II/C-M).The concrete with CEM II/A-M (V-LL) reacts slightly more sensitive to water dosage variations.A more pronounced strength decrease is observed at the age 28 d. No significant effect of cement type or water dosage variation on the elastic modulus of the concretes could be observed, despite significant differences in compressive strength.It should be noted that the values of elastic moduli were determined after 28 days and thus at a relatively early stage of hydration.Especially for concretes with CEM III/A and CEM II/C-M with blast furnace slag, a significant increase in both compressive strength and elasticity modulus can be expected due to the blast furnace slag. Bleeding of fresh concrete is strongly affected by temperature.At 10 °C, there is a clear dependence on the cement type.The concrete with CEM III/A shows the highest and the concrete with CEM II/C-M (V-LL) the lowest amount of bleeding water.
The study at hand was able to show that clinker-efficient cements with high contents of granulated blast furnace slag or fly ash and limestone (CEM II/C-M) are suitable for the production of concrete that are commonly used in practice for construction of indoor elements (XC1) or elements in protected outdoor environment (XC3) under practical boundary conditions.Concretes made with CEM II/C-M (V-LL) or CEM II/C-M (S-LL) exhibit similar fresh and hardened properties as the reference concrete with CEM III/A with an equal clinker content (≈ 50 wt.%).

Figure 2 Figure 3
Figure 2Consistency for all concretes investigated at 20 °C as a function of w/c-ratio (different w/c-ratios result from systematic variations in water content to simulate unknown variations in the water content) Figure 3 Rheological response (yield stress as a function of plastic viscosity) to simulate unknown variations in the water content from the target value

Figure 4 Figure 5
Figure 4Maximum bleeding water for all concretes investigated at 20 °C as a function of w/c-ratio (different w/c-ratios result from systematic variations in water content to simulate unknown variations in the water content from the target value) Figure5Compressive strength fc,cube for all concretes investigated at 20 °C as a function of w/c-ratio (different w/c-ratios result from systematic variations in water content to simulate unknown variations in the water content from the target value)

Table 1
Concrete mixture (reference composition without variation)

Table 3
Mixing regime

Table 2
Physical properties of cements