Characterization of the cements / Monitoring of temperatures reached by the pile caps.
In this section is presented the experimental program this research, which describes all methods of instrumentation and monitoring the temperature of the pile caps, the characteristics of concrete and materials used in confection these and the equipments and experimental procedures used to perform the test Duggan. Still, in order to comply to the objectives proposed in this researc
3.1 Monitoring of temperatures reached by the pile caps.
This Was realized randomly through the monitoring of the evolution of the temperature in a total of five pile caps foundation, scattered in four works attended for three ready mix concrete plants of the region.
The evolution curves of temperature x time of the concretes were obtained through instrumentation, by means of datalogger and thermocouples. A portable digital datalogger (Figure 2a) was used, model TM-947SD, manufactured by Lutron Electronic, with ability of four channels to thermocouple, resolution 0.1°C, with programmed frequency for data acquisition every 10 min over approximately 7 days.Four thermocouples type "K" were used with exposed joint (Figure
The evolution curves of temperature x time of the concretes were obtained through instrumentation, by means of datalogger and thermocouples. A portable digital datalogger (Figure 2a) was used, model TM-947SD, manufactured by Lutron Electronic, with ability of four channels to thermocouple, resolution 0.1°C, with programmed frequency for data acquisition every 10 min over approximately 7 days.Four thermocouples type "K" were used with exposed joint (Figure
2b), each with a total length of 5 m, three of which were allocated in specific positions of the pile caps: near the bottom, in the central core and near the surface.
The remainder thermocouple was allocated outside the pile cap, with the objective of obtaining data of ambient temperature. Metal pipes were needed to aid in the correct placement and reuse of the thermocouple cables. In all cases it was obtained the average temperature of the concrete at the time of casting, by means of a digital thermometer auxiliary TM-364 model, manufactured by the Tenmars, with capacity of two channels for thermocouple, resolution of 0.1°C (Figure 2c). The details about the composition of the concretes used in the pile caps in study are shown in Table 5. Already the geometric details (in meters) and the allocation points of the thermocouples in each pile cap are shown in sketch and real, in Figures 3 and 4, respectively.
The remainder thermocouple was allocated outside the pile cap, with the objective of obtaining data of ambient temperature. Metal pipes were needed to aid in the correct placement and reuse of the thermocouple cables. In all cases it was obtained the average temperature of the concrete at the time of casting, by means of a digital thermometer auxiliary TM-364 model, manufactured by the Tenmars, with capacity of two channels for thermocouple, resolution of 0.1°C (Figure 2c). The details about the composition of the concretes used in the pile caps in study are shown in Table 5. Already the geometric details (in meters) and the allocation points of the thermocouples in each pile cap are shown in sketch and real, in Figures 3 and 4, respectively.
3.2 Characterization of the cements
To realize this step was collected in ready mix concrete plants A, B and C all materials (cement, fine aggregate, coarse aggregate, mineral additions) used as inputs to the concretes in question. In the same period they were also collected the clinker in the cement factories.
3.2.1 Chemical composition of the cements and their respective clinkers - XRF
Figure 2 Instrumentation used to monitoring of temperatures reached by the pile caps: a) Portable digital datalogger, b) Termocouple, c) Digital thermometer auxiliary
To determine the chemical composition of oxides of the cements and the potential composition of their respective clinkers were realized chemical analysis by fluorescence X-ray (XRF) in mineralogy laboratory of the Associação Brasileira de Cimento Portland (ABCP).
3.2.2 Density and Blaine fineness
This step of the characterization was performed in the laboratory Portland cement of TECOMAT - Tecnologia da Construção e Materiais. The density of cement were obtained according method specified in NBR NM 23 - Cimento Portland e outros materiais em pó - Determinação da massa específica (ABNT [22]).
To obtain the specific surfaces of the cements, we used the method specified in NBR NM 76 - Cimento Portland - Determinação da finura pelo método de permeabilidade ao ar (Método de Blaine) (ABNT [23]).
3.2.3 Duggan Test
Was utilized the Duggan test as testing methodology for the detection of potential deleterious expansion in the studied concretes due to DEF, because it is a fast method that lasts only 30 days and that will replace the method proposed by the LCPC, which lasts at least 1 year. It is noteworthy that the expansion in Duggan test is not due to AAR or recovery from drying shrinkage, caused by the thermal cycle through by water absorption on immersion. The main cause of expansion measured in the test is assigned to the DEF (GRABOWSKI et al. [20]). A flowchart of the sequence of activities performed in this research of the Duggan test is shown in Figure 5. The whole procedure described below was applied to the materials used distinctively for the three studied ready mix concrete plants, incorporating additions commonly found in the region, metakaolin (8% and 16%) and silica fume (5% to 10%), all substituting weight of the cement (o.w.c.), aiming their evaluation as to the potential mitigation of the expansions. As a matter of national standardization, in this work we were used molds whose dimensions are 100 x 100 x 400 mm and coarse aggregates were crushed and screened in fractions 12.5, 9.5 and 4.75 mm, unlike the original method which provides prisms of 75 x 75 x 350 mm and coarse aggregate crushed and screened in fractions of 14, 10 and 5mm. The temperature in the test room was maintained at 23±2°C. For crushing, was used a jaw crusher, MAQBRIT brand, BM 10x6 model. As prescribed by test method (GRABOWSKI et al. [20]), the concrete mix parameters are the following: cement = 475 kg/m3; coarse aggregate into three fractions of 292 kg/m3 each (total = 876 kg/m3); fine aggregate=656 kg/m3; w/c ratio = 0.40; and slump = 80±10 mm. All fine aggregates used in the assay were dried at 105°C. The coarse aggregates were used in the saturated surface dry (SSD) condition. The aggregates were broken up and bagged
Table 5 Details of the concretes composition used in the manufacture of the pile caps in the study
Figure 3 Geometric details of the pile caps and allocation of the thermocouples: a) Pile cap 1, b) Pile cap 2, c) Pile cap 3, d) Pile cap 4, e) Pile cap 5
Figure 4 Real details of the geomety of the pile caps and allocation of the thermocouples: a) Pile cap 1, b) Pile cap 2, c) Pile cap 3, d) Pile cap 4, e) Pile cap 5
in quantities sufficient to make moldings of 15 concrete prisms and their individual slump measures.
In order to avoid loss of material, was used a planetary mixer of big volume to replace the common mixer. Cements, additions and water were weighed at the time of molding. All dried material was pre-homogenized manually with the aid of spatula and the time chosen mechanical mixing was set so as to obtain homogeneity in the mixtures: 2 min at low speed followed by 2 min at high speed. Because of the slump specified in 80±10 mm, it was used superplasticizer 3rd generation polycarboxylate-based for possible fixes of slump. The additive dosages ranged between 0.0 and 0.6% on weight of cement.
Figure 6 Steps of the Duggan test: a) Extraction of the concrete cores through drill Hilti, b) Thermal cycle used in the Duggan method (GRABOWSKI et al [20]), c) Equipment provided with dial indicator to realization of the expansion readings of the concrete cores
It was used immersion vibrator in consolidation and molding of prisms. The mold was filled with only one layer of concrete and was consolidated at three equidistant points along the prism. After molding, the prisms were subjected to accelerated thermal cure after 2-hour pre-cure at room temperature. The accelerated conditions include a ramp at 2 h the temperature reaches 85°C and then remain 4 hours at 85°C, followed by cooling to room temperature overnight in the oven. At the end of the thermal cure, all prisms followed for release and extraction of 5 cores on each prism. The extraction of the concrete cores was performed with the aid of Hilti drill machine and diamond drill, as shown in Figure 6a.
The Duggan method establishes the dimensions of the concrete core: 25 mm in diameter and 50±5 mm long. Thus, at the end of extraction, all concrete cores went for preparing. It was done the cut with help of jig and diamond saw in order to framing in the specified length. Posteriorly the holes are made in each core, with the aid of a jig, adapted in a bench drill so that they were maintained plumb and the absence of eccentricity. Made the holes, all concrete cores were dried with compressed air pistol aid.
After drying, it was verified with the aid of caliper rule the depth of each hole so that it was obtained the effective gauge length, equivalent to the internal distance between the ends of the pins. The steel pins of low coefficient of thermal expansion (≤2x10-6°C-1)were fixed to the concrete cores by means of 330 Loctite adhesive, which has methacrylates as chemical base. The choice of this adhesive was made taking into account the cycles of wetting/drying and heating/cooling, proposed in Duggan test (GRABOWSKI et al. [20]), as shown in Figure 6b.
Fixed pins, the concrete cores remained immersed in distilled water for 3 days, and then being subjected to 3 cycles of heating/ cooling and wetting/drying, specified in Duggan test, during for a period of 7 days.
On completion of the cycle, the cores are then immersed in distilled water and measurements are performed during 20 days. Concrete cores tested by the method Duggan, which expand 0.05% or more after this time, indicate that the concrete has potential for deleterious expansion triggered by DEF (GRABOWS-
KI et al. [20]).
Table 6 Comparative summary of characteristics and thermal properties of the monitored concretes
| Characteristics | Pile cap 1 | Pile cap 2 | Pile cap 3 | Pile cap 4 | Pile cap 5 |
| Cement type | X (CP II E 40) | X (CP II E 40) | X (CP II E 40) | Y (CP II F 32) | Z (CP V ARI RS) |
| Cement content (kg/m3) | 400 | 400 | 361 | 369 | 430 |
| fck (MPa) | 50 | 50 | 40 | 40 | 40 |
| Maximum temperature (°C) | 72.7 | 75.0 | 75.0 | 73.7 | 75.3 |
| Maintainability time - T≥70°C (h) | 19.1 | 46.5 | 42.7 | 27.1 | 31.2 |
| Average temperature of casting (°C) | 34.6 | 35.1 | 33.0 | 35.3 | 35.4 |
| Thermal gradient (°C) | 38.1 | 39.9 | 42.0 | 38.4 | 39.9 |
| Coefficient of thermal efficiency (°C/kg/m3) | 0.095 | 0.100 | 0.116 | 0.104 | 0.093 |
| Rate of pre-peak gain (°C/h) | 1.958 | 1.836 | 1.447 | 2.798 | 1.654 |
| Rate post-peak loss (°C/h) | 0.273 | 0.204 | 0.270 | 0.322 | 0.271 |
During the final period of immersion in distilled water, were realized the expansion readings.
To perform these readings, it is shown in Figure 6c, the device used gifted of digital dial indicator, Mitutoyo brand, with a sensitivity of 0.001 mm and standard calibrator of nominal length of 80 mm, to perform the zeroing each set of 5 concrete cores. The testimonies were removed one by one of the distilled water and dried with towel. The reading was done making it a 360º spin in concrete core, in a counterclockwise direction, making the reading of the smallest value in the dial indicator.
4. RESULTS AND DISCUSSIONS
In this chapter are presented the results of the experimental procedure, as well as their analysis, which are geared towards the general objective of this research, confirming or not the hypothesis lifted.
4.1 Monitoring of temperatures reached by the pile caps
Follows in Table 6, a comparative summary of the thermal properties related to 5 pile caps of foundation monitored.
The Figure 7a presents the evolution graph of temperature versus time, referring to the pile cap of foundation 1.
The average temperature of the concrete at the time of casting was 34.6°C. As expected, the highest temperature was recorded at point allocated in the core of pile cap 1.
The peak temperature was 72.7°C and the maintainability time of the temperatures above 70°C was approximately 19.1 h. As the cement content was 400 kg/m3 and the thermal elevation gradient of 38.1°C, has a coefficient of thermal efficiency of approximately 0.095°C/kg/m3.
Due to the low thermal conductivity of the concrete, the linear low rate of post-peak losses in the core was approximately 0.273°C/h or 6.56°C/day. The rate of pre-peak gain on the core was approximately 1.958°C/h.
The Figure 7b presents the evolution graph of temperature versus time, referring to the pile cap of foundation 2.
In this case, the mean temperature of the concrete at the time of release was 35.1°C. As in pile cap 1, the highest temperature of pile cap 2 was recorded at point allocated in its core. The peak temperature was 75.0°C and the maintainability time of the temperatures above 70°C was approximately 46.5 h, value well above than the pile cap 1, possibly attributed to the greater volume of concrete of pile cap 2. As the cement content was 400 kg/m3 and the thermal elevation gradient of 39.9°C, has a coefficient of thermal efficiency of approximately 0.100°C/kg/m3.
The linear rate post-peak losses in the core was approximately 0.204°C/h or 4.90°C/day, lower value than that occurring in the pile cap 1. The rate of pre-peak gain on the core was approximately 1.836°C/h.
Figure 7 Graphs of evolution of temperature x time: a) Pile cap 1, b) Pile cap 2, c) Pile cap 3, d) Pile cap 4, e) Pile cap 5
The Figure 7c presents the evolution graph of temperature versus time, referring to the pile cap of foundation 3.
In this case, the mean temperature of the concrete at the time of release was 33.0°C. As in previous pile caps, the highest temperature was recorded at point allocated in its core of the pile cap. The peak temperature was 75.0°C and the maintainability time of the temperatures above 70°C was approximately 42.7 h.
Despite the smaller volume of concrete, this value shows up well above of the maintainability time of pile cap 1. As the cement content was 361 kg/m3 and the thermal elevation gradient of 42.0°C, has a coefficient of thermal efficiency of approximately 0.116°C/kg/m3.
The linear rate post-peak loss in the core was approximately 0.270°C/h or 6.47°C/day. The rate of pre-peak gain on the core was approximately 1.447°C/h.
The Figure 7d presents the evolution graph of temperature versus time, referring to the pile cap of foundation 4.
The average temperature of the concrete at the time of release was 35.3°C. The highest temperature was also recorded at point allocated in its core of the pile cap.
The peak temperature was 73.7°C and the maintainability time of the temperatures above 70°C was approximately 27.1 h. As the cement content was 369 kg/m3 and the thermal elevation gradient of 38.4°C, has a coefficient of thermal efficiency of approximately 0.104°C/kg/m3.
The linear rate postpeak loss in the core was approximately 0.322°C/h or 7.72°C/ day. The rate of pre-peak gain on the core was approximately 2.798°C/h.
Table 7 Chemical and mineralogical composition of the clinkers X, Y and Z
| CaO | 63.11 | 61.00 | 59.54 |
| SiO2 | 19.44 | 18.22 | 17.90 |
| Al2O3 | 5.51 | 4.62 | 3.51 |
| Fe2O3 | 2.92 | 2.52 | 3.45 |
| SO3 | 1.98 | 1.92 | 1.94 |
| MgO | 3.14 | 4.73 | 10.32 |
| TiO2 | 0.24 | 0.31 | 0.23 |
| SrO | 0.06 | 0.06 | 0.09 |
| P2O5 | 0.32 | 0.27 | 0.15 |
| MnO | 0.03 | 0.02 | 0.05 |
| K2O | 1.29 | 0.63 | 0.94 |
| Na2O | 0.06 | 0.11 | 0.12 |
| Loss on ignition | 0.76 | 4.48 | 0.59 |
| Total | 98.86 | 98.89 | 98.83 |
| Na2O Equivalent* | 0.91 | 0.52 | 0.74 |
| LSF* (Lime Saturation Factor) 100.27 104.81 | 105.24 | ||
| SM* (Silica Module) | 2.306 | 2.552 | 2.572 |
| AM* (Alumina Module) | 1.887 | 1.833 | 1.017 |
| C3S Bogue | 67.91 | 75.15 | 77.77 |
| C2S Bogue | 4.53 | -4.43 | -7.33 |
| C3A Bogue | 9.66 | 7.98 | 3.46 |
| C4AF Bogue | 8.89 | 7.67 | 10.50 |
(*): Na2O Equivalent = Na2O + 0,658.K2O; LSF = CaO.100/(2,8.SiO2 + 1,2.Al2O3 + 0,65.Fe2O3); SM = SiO2/(Al2O3 + Fe2O3); AM = Al2O3/Fe2O3 .
The Figure 7e presents the evolution graph of temperature versus time, referring to the pile cap of foundation 5.
The average temperature of the concrete at the time of release was 35.4°C. The highest temperature was also recorded at point allocated in its core of the pile cap. The peak temperature was 75.3°C and the maintainability time of the temperatures above 70°C was approximately 31.2 h. As the cement content was 430 kg/m3 and the thermal elevation gradient of 39.9°C, has a coefficient of thermal efficiency of approximately 0.093°C/kg/m3. The linear rate postpeak loss in the core was approximately 0.271°C/h or 6.51°C/ day. The rate of pre-peak gain on the core was approximately 1.654°C/h.
It is notorious that in all cases, without exception, the pile caps reached temperatures above 70°C, able to achieve the level of 75°C, regardless of factors such as type and cement content, system type of form used, the volume of the concreted element, etc. Still, as mentioned, the high temperatures have a fundamental role in the DEF and is widely accepted in the technical means which the concrete is susceptible to triggering this, when subjected to temperatures above 65-70°C [4, 5, 7, 8]. Therefore, of the thermal point of view, all the pile caps exceed the safe limit of temperature and therefore, are in a critical situation with respect to DEF.
Table 8 Chemical composition of the cements X, Y e Z
| Determinations | Cement X (%) | Cement Y (%) | Cement Z (%) |
|---|---|---|---|
| CaO | 56.72 | 62.25 | 63.40 |
| SiO2 | 20.13 | 18.65 | 19.04 |
| Al2O3 | 5.47 | 4.41 | 5.01 |
| Fe2O3 | 2.54 | 3.87 | 3.86 |
| SO3 | 3.55 | 3.28 | 3.04 |
| MgO | 3.29 | 0.52 | 0.62 |
| TiO2 | 0.28 | 0.25 | 0.25 |
| SrO | 0.06 | 0.24 | 0.01 |
| P2O5 | 0.37 | 0.22 | 0.02 |
| MnO | 0.17 | 0.14 | 0.06 |
| K2O | 1.02 | 0.49 | 0.22 |
| Na2O | 0.09 | 0.07 | 0.04 |
| Loss on ignition | 5.50 | 4.78 | 3.97 |
| Total | 99.19 | 99.17 | 99.54 |
| Na2O Equivalent* | 0.76 | 0.39 | 0.18 |
(*): Na2O Equivalent = Na2O + 0,658.K2O .
4.2 Characterization of the cements
4.2.1 Chemical composition of the cements and their respective clinkers - XRF
The results for the clinkers respectives of the cements are shown in Table 7. Note that the SO3 content in all the clinkers were very close and worth approximately 2%. As for the alkali content, there is a higher content in the X clinker, which possibly will reflect in the alkalis content of their respective cement.
As expected, the Z clinker, used in the manufacture of cement CP V ARI RS, presented higher C3S content before others. However, this aspect not fundamentally reflected in the peak temperatures values reached by the monitored pile caps foundation, although the pile cap 5 made from this cement showed the highest peak temperature among them.
In respect to the negative C2S content, it is a reflex from the use of a SCF greater than 100, meaning that the CaO content in the clinker is higher than necessary, or even there no SiO2, Al2O3 and sufficient Fe2O3 to react with CaO for the formation of basic compounds.
The X, Y and Z clinkers presented the total C3A content of 9.66%, 7.98% and 3.48% respectively. The high values presented by clinkers X and Y may contribute to the DEF, and therefore, for the values for expansion of Duggan test. It is worth noting the low value presented by the Z clinker, which does not contribute in the ettringite formation compared to other clinkers.
The results for the cements are shown in Table 8. Note that the high content of SO3 (> 3%) in all cements studied, being higher for the X cement (CP II E 40), which may influence the values of expansion obtained in the Duggan test. It is the X cement that also has the highest equivalent alkali content, a value well discrepant compared to others cements (0.76% for the X cement against 0.39% and 0.18% for Y and Z cements, respectively). The amount of Fe2O3 is very similar in the cements Y (CP II F 32) and Z (CP V ARI RS), being well below in the X cement. This may result in greater susceptibility of the X cement to attack by sulfates due to DEF.
4.2.2 Density and Blaine fineness
The cements studied did not show great variation between their densities.
The Z cement (CP V ARI RS), showed higher fineness compared to the other cements. On the other hand, the X cement (CP II E 40) presented specific area much lower than the others, contrary to what was expected, because it is a class cement 40 and which requires a greater degree of grinding.
It is known that cement fineness is related to their reactivity, whereas, how much the thinner cement, the greater the contribution to the increase of the heat of hydration this (Mehta and Monteiro [10]). Although the rate pre-peak gain of temperature was higher in pile cap 4, which used Y cement in its constitution, there was no significant correlation between the thermal behavior of the concretes and the fineness of its cements, since there are other influential aspects in the thermal behavior of these elements. The results obtained of density and Blaine fineness are shown in Table 9.
4.2.3 Duggan test
The Figure 8a shows the graphic of the average expansion of 5 concrete cores versustime referring to the cement X (CP II E 40).
Table 9 Densities and specific surfaces areas of the cements studied
| Cement X | Cement Y | Cement Z | |
| Density ρ (g/cm3) | 3.04 | 3.02 | 3.06 |
| Specific surface area S (cm2/g) | 3890 | 4670 | 4870 |
It is notorious as the high degree of expandability of the case X0, whose value at 20 days was 0.146%, well above the 0.05% limit specified by Duggan. This level of expansion was mitigated with use of mineral additions (metakaolin and silica fume), being lower in the case X10S, whose expansion was 0.058%, resulting in a 60% reduction in the average expansion of reference. The expansion undergone by the concrete in the Duggan test confirms the analysis of chemical composition of this cement and their respective clinker. This degree of expansion can be attributed to various factors, such as: high C3A content (9.66%) present in the X clinker and high contents of SO3 and alkalis in the X cement (3.55% and 0.76%, respectively).
In Duggan test made with the Y cement (CP II F 32), the greatest degree of expansion occurred in the case Y0, as shown in Figure 8b, where the value at 20 days was 0.053%, also above the limit of 0.05% imposed by Duggan. The mineral additions also proved effective in the mitigation of the expansions, being lower in the case Y10S, whose expansion was 0.024%, resulting in a 55% reduction in the average expansion of reference.
Figure 8 Graphs of the average expansion of the 5 concrete cores versus time: a) Cement X (CP II E 40), b) Cement Y (CP II F 32), c) Cement Z (CP V ARI RS)
The expansion undergone by the concrete in the Duggan test also confirms the analysis of chemical composition of this cement and their respective clinker. Despite the high C3A content (7.98%) present in the Y clinker and of the SO3 content exceeding 3% (3.28%), this has a low alkali content (0.39%), contributing to lower solubility of the ettringite and thus, to a greater impediment of the triggering of the DEF.
Already the Z cement (CP V ARI RS), the best was that behaved in Duggan test between sealers tested, according to the results shown in Figure 8c. Is notorious which this was the only cement, that no additions, showed lower expandability, although close to the 0.05% limit imposed by Duggan, whose value at 20 days were 0.044%. The lowest level of expansion also gave in the case Z10S whose expansion was 0.021%, resulting in a 52% reduction in the average expansion of reference.
The low level of expansion experienced by the concrete in Duggan test confirms essentially the chemical composition analysis of this cement and of their respective clinker. While treating of a cement CP V ARI, this being a tough cement to sulfates was which showed the smallest contents of compounds that enable the triggering of the DEF: low content of C3A (3.46%) present in the Z clinker and low contents of SO3 and alkalis in the Z cement (3.04% and 0.18%, respectively).
4.2.4 Framing of the pile caps in the LCPC guide
To better awareness of that the pile caps foundation of the Recife metropolitan region are critical regarding the DEF, these were framed in LCPC guide.
The 5 pile caps studied were classified in category II of the guide, which the consequences of a potential disorder would be quite serious. As for the exposure class, they were designated in XH3 class, which covers foundations that have lasting contact with water. Consequently, a Cs level of prevention is established in relation to the DEF, which establishes that the maximum temperature reached in the concrete is 70°C and, if not possible, this should never exceed 80°C and must satisfy at least one of the conditions of use set forth in Table 4. In Table 10, are presented the details of the framing of each pile cap.
The peak of temperature recorded in pile cap 1 was 72.7°C, while that in pile caps 2 and 3, these were equal to 75.0°C. Thus, it was not satisfied the Cs level of prevention expected. However, the value of 80°C was not exceeded and allows them to be evaluated according to the conditions of use.
The temperature maintainability time in the concrete of the pile caps 1, 2 and 3 was 19.1 h, 46.5 h and 42.7 h, respectively. All extrapolate the 4h limit allowed by the condition I, justifying the unsatisfactory condition.
It is noteworthy which the equivalent alkali content of 3.04 kg/m3 present in pile caps 1 and 2, which exceeds the limit value of 3 kg/ m3. In pile cap 3, the value of alkalis is 2.74 kg/m3 and is well close to the threshold. The condition II is not satisfactory due to the fact that this cement will not be RS class and, according to manufacturer's information, has blast furnace slag content of around 16%. The contents of 3.55% of SO3 in the cement and 9.66% of C3A in the clinker exceeds the limits of 3% for the SO3 in the cement and 8% for the C3A in the clinker, does not satisfying the conditions III and IV.
Related to condition V, was taken into account the Duggan test carried out on the cement without the use of additions, so that they obtained average value was 0.146% and this exceeds the limit of 0.05% proposed by Duggan. However, it is important to note that the incorporation of mineral additions had mitigator effect in the expansions assigned to the DEF. The condition VI is not applicable because it is not precast element.
Table 10 Framing of the pile caps fundation in the LCPC guide
| Tmax (°C) | 72.7 | 75.0 | 75.0 | 73.7 | 75.3 |
| tmaintainability (h) | 19.1 | 46.5 | 42.7 | 27.1 | 31.2 |
| Alkali content equivalent (kg/m³) | 3.04 | 3.04 | 2.74 | 1.44 | 0.77 |
| Type of cement | CP II E 40 | CP II E 40 | CP II E 40 | CP II F 32 | CP V ARI RS |
| SO3 of the cement (%) | 3.55 | 3.55 | 3.55 | 3.28 | 3.04 |
| C3A of the clinker (%) | 9.66 | 9.66 | 9.66 | 7.98 | 3.46 |
| Duggan test (%) | 0.146 | 0.146 | 0.146 | 0.053 | 0.044 |
| Condition of use | Situation | ||||
| I | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory |
| II | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory |
| III | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory |
| IV | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory |
| V | Unsatisfactory | Unsatisfactory | Unsatisfactory | Unsatisfactory | Satisfactory |
| VI | Not applicable | Not applicable | Not applicable | Not applicable | Not applicable |
In pile cap 4, the peak of temperature was 73.7°C. Thus, it was not satisfied the Cs level of prevention expected. However, the value
of 80°C also was not exceeded and allows them to be evaluated according to the conditions of use established in Table 4.
The temperature maintainability time in the concrete of the pile cap 4 was 27.1 h, which far exceeds the 4-hour limit allowed by the condition I, justifying the unsatisfactory condition. The condition II is not satisfactory due to the fact of this type of cement will not be accepted for concrete molded in loco. The contents of 3.28% of SO3 in the cement exceeds the limit value of 3% and the value of 7.98% of C3A in clinker equals to limit value of 8%, so that does not meet the conditions III and IV.
Related to the condition V, was taken into account the Duggan test carried out on the cement without the use of additions, so that they obtained average value was 0.053% and this exceeds, although very close, the limit of 0.05% proposed by Duggan. However, it is important to note that the incorporation of mineral additions also had a mitigator effect in the expansions assigned to the DEF, including being smaller than the reference value set by Duggan. The condition VI is also not applicable because it is not precast element.
In pile cap 5, the peak of temperature was 75.3°C. Thus, it was not satisfied the Cs level of prevention expected. However, the value of 80°C also was not exceeded and allows it to be evaluated according to the conditions of use established in Table 4.
The temperature maintainability time in the concrete of the pile cap 5 was 31.2 h, which greatly exceeds the limit of 4h permitted for the condition I, justifying the unsatisfactory condition. The condition II is not satisfactory due to the fact of this type of cement will not be accepted for concrete molded in loco. The condition III is not satisfied, because it is not cement CP III or CP IV and the SO3 content in this cement was 3.04%, surpassing, even a little, the limit value of 3%.
It is important to note the very low C3A content in clinker (3.46%). Related to the condition V, the average value obtained in Duggan test was 0.044%, being the only one among the cements studied, than remained below the limit value without the use of mineral additions. Still, incorporation of additions also had a mitigator effect on expansions assigned to the DEF. The condition VI, as in all other cases, it is not applicable because it is not precast element.
5. In CONCLUSIONS
The results of the present study confirm the risk of triggering of the DEF in foundation pile caps of the metropolitan region of Recife. All factors related to thermal properties and chemical composition of the concretes used in the region converge for a condition of ideal susceptibility in triggering DEF these elements.
All the pile caps, without exception, exceeded the safe limit of 70°C, and still, they remained many hours above this limit, exceeding the value of 4h defined in LCPC preventive guide. The level of peak temperatures of these showed no dependence on factors such as type, fineness and cement content, lithological type of aggregate, type of formwork system used, volume of concreted element, etc. As for the chemical composition of X cement (CP II E 40) was which showed the higher content of C3A in clinker and SO3 and equivalent alkalis in the cement, so that these factors were of fundamental importance in the susceptibility to DEF of the concrete made with this cement. This fact was confirmed by the level of expansion of 0.146% presented at Duggan test.
Surprisingly, despite being a cement with a low content of additions, the Z cement (CP V ARI RS) was the only approved in Duggan test without the use of additions of metakaolin or silica fume. This is attributed to the low content of C3A in the clinker (3.46%) and SO3(3.04%) and equivalent alkali (0.18%) in the cement. Regardless of the content and type of cement, the mineral additions showed potential of mitigation of expansions assigned to the DEF. In general, the fume silica showed to be more effective than metakaolin, regarding to the reduction of the expansion due to the DEF in the concrete cores.
Due to the difficulty in the control of chemical parameters related to the cements, principally in constructions of small size of a pile it is critical, in preventing DEF, the awareness of the thermal question and the establishment of the use of cements of the types CP III and CP IV, the possibility of reducing of the fck and cement content in the concrete, realization of the concreting of the elements by layers and until precooling of concrete with the use of ice in partial substitution of the water. Conclusively, it is important the specification at design of minimum and basics requirements to avoid high temperatures in these concrete massive elements, preventing the delayed ettringite formation.
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