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Received on July 07, 2017; Approved on November 19, 2017.
Through this document, the design and manufacture of a prototype of a chamber with humidity and temperature variations for curing alkaline activation concretes made from mixtures of steel slag and flying ash is presented, to be mounted directly on site, this benefits the industrial sector in the development of new projects by improving performance, reducing risks and transportation costs in the manufacturing processes of these materials that are currently present. The device requires the integration of distinct mechanical and electronic elements along with knowledge in the control and programming area for its correct operation, with the degree of precision necessary to guarantee optimal levels of resistance in the different types of concrete by alkaline activation, emanating from the design and the right choice of materials for the construction of the chamber.
Keywords:curing, humidity, temperature, modular, concrete, slag, ash
El estudio realizado da a conocer el diseño y fabricación de un prototipo modular a escala, de una cámara con variación de humedad y temperatura para curado de concretos de activación alcalina; elaborado a partir de mezclas de escoria siderúrgica y cenizas volantes, para ser montado directamente en obra; el estudio beneficia al sector industrial en el desarrollo de nuevos proyectos a dado que permite mejorar el desempeño, reducir riesgos y costos de transporte en los procesos de fabricación de los materiales que se presentan en la actualidad. El dispositivo requiere de la integración de distintos elementos mecánicos y electrónicos junto con conocimientos en el área del control y la programación para su correcto funcionamiento, además, es necesario un grado de precisión para garantizar niveles óptimos de resistencia en los diferentes tipos de concreto por activación alcalina, a partir del diseño y la buena elección de los materiales en la fabricación de la cámara.
Palabras clave:curado, humedad, temperatura, modular, concreto, escoria, ceniza
Regarding to the technical problems of the traditional Portland
cement concrete, it is worth to remark those related to
durability, reinforcement corrosion, frost resistance, sulfate
attack, carbonation, and so on. [1-2]. Thus, with the aim
focused in contributing to the reduction of gas emissions into
the atmosphere and to solve the problems of durability of
Portland cement, it has been proposed the use of partial mineral
additions to cement such as fly ash and blast furnace slag,
whose manufacture does not generate a high energy
consumption; and also it doesn´t emit too high polluting gases
volumes and its filler effect and pozzolanic reaction help
mitigate problems of conventional concrete durability [3].
In that sense, the Colombian metallurgical and energy industry
generates substantial amounts of alternative raw materials to
the cement (fly ash and steel slag), however, most of these are
not fully exploited. In particular for each ton of coal that is
burnt into a thermoelectric power plant, approximately 200 kg
of fly ash are produced, and the consumption of the pulverized
coal causes environmental problems due to the accumulation of
fly ash in areas close to large deposits [4].
The ground granulated blast furnace slag (GBFS) and fly ash
have been used traditionally as a partial substitute for ordinary
portland cement within concrete mixtures, resulting in materials
with comparable mechanical performance to blends 100%
Portland cement [5]. Therefore, due to the increasing production
at national and global levels of fly ash and blast furnace
slag, it is necessary a higher recycling of these products. For
this reason, the way of valorization of these residues can be its
use for the total replacement of Portland cement in alternative
concrete mixtures via alkaline activation.
Currently, the two big precursors for alkaly activated binders
are blast furnace slag and fly ash from power plants and steel
industry respectively, which are combined with chemical
activators (hydroxides + silicates), provoking the transformation
to particular gels with mechanical properties
(aluminosilicate and calcium silicate hydrated gels) with a
amorphous or semicrystalline configuration [4], [6]. In general,
the curing of these alkali activated materials requires high
temperatures, about 80 and 60 ° C and relative humidity around
90% in a period of 24 hours. Currently the curing of these materials
is carried out in specialized laboratories, due to the lack of
curing methods that can be applied directly on site.
However, these curing conditions results practical for applications
in plant for the production of prefabricated [7].
As mentioned, traditional methods for conventionally concrete
curing in the construction field are oriented using readily wet
environments, while for alkaly activated materials, curing
procedures at high humidities and temperatures increase its
transportation costs and limit its applicability. Consequently,
this paper studies the design and manufacture of a chamber
automated, modular curing, and which can be applied directly
on site, to manufacture elements of various sizes by means
alkaline activation [8].
The equipment mechanism proposed is to vary and monitor
temperature conditions (up to 80 ° C) and moisture (up to 90%
relative humidity) required for the curing process, in order to
ensure a reduction in transport costs of alkaline activation
material from the plant to the work. In this sense, by applying
the technology of alkali activation, industrial wastes such as fly
ash and blast furnace slag can be appropriately exploited and
transformed into new materials with low energy consumption,
characterized by presenting high durability and excellent
mechanical performance [9].
Structural planning Several ideas were generated in terms of how to address the challenge of applying the curing process in a place other than a laboratory, so the conditions applicable in this particular case of environment differed from those applied in the laboratory, especially concerning the geometry which can be variable. In that sense, a modular solution that fitted to the geometry of the building, and also be easy to assemble and deject was proposed.
Based on the set conditions, the idea of a lamellar structure of low weight, assembled by plates bolted joint was raised, but the idea was dropped since the weight of the sheets and in some cases the height of the structure would be factors affecting its stability. For this reason, the need for the structure had structural support elements in which it was decided to allow the splined coupling studs of the sheets (Fig.1 )
Focused on the aim of the project, that is, making a prototype,
it was suggested that the geometry of this was adapted to the of
size three mortar cubes (50x50x50 mm), and the measures
presented were defined in the planes found in the attachments
to this document [10].
The process of delineating the prototype elements planes was
carried out by the mechanical design software SolidWorks,
which allowed to notice that for the sheets coupling with the
studs support, small channels at the ends became necessary of
the main perpendicular to the longitudinal channels pareles to
avoid mismatch dimensions by interference material.
Furthermore, analyzing the binding form between studs
support and blades, it became clear that simply attaching the
blades into the slots of the uprights wasn’t enough since these
connections generate a considerable amount of leakage; this
situation impedes generation controlled environment as
required for this purpose a sealed or otherwise with the least
amount of leakage cavity, since these increase the amount of
loss and result in defects in the curing process; From this,
several options were discussed with the aim of reducing the
number of leaks in the joints.
Focused on the aim of the project, that is, making a prototype,
it was suggested that the geometry of this was adapted to the of
size three mortar cubes (50x50x50 mm), and the measures
presented were defined in the planes found in the attachments
to this document [10].
The process of delineating the prototype elements planes was
carried out by the mechanical design software SolidWorks,
which allowed to notice that for the sheets coupling with the
studs support, small channels at the ends became necessary of
the main perpendicular to the longitudinal channels pareles to
avoid mismatch dimensions by interference material.
Furthermore, analyzing the binding form between studs
support and blades, it became clear that simply attaching the
blades into the slots of the uprights wasn’t enough since these
connections generate a considerable amount of leakage; this
situation impedes generation controlled environment as
required for this purpose a sealed or otherwise with the least
amount of leakage cavity, since these increase the amount of
loss and result in defects in the curing process; From this,
several options were discussed with the aim of reducing the
number of leaks in the joints.
Selection of structural materials
Taking as reference points
the requirements of the curing process (working temperature
between 60 and 80 ° C and a moisture of 90% for periods of 24
hours), the dimensional constraints imposed in the planning
stage, and further having consider the logistical conditions of
use of the prototype, which are the characteristics of a civil
work, immediately discarded metallic materials, since the cost
of these, with the required dimensions was high, and the weight
of some of these negative impact on the prototype modular and
versatile concept; this without difficulty would control
moisture and temperature in a cavity with metal walls, since the
capacity of water absorption and high thermal conductivity of
these materials, would generate a rapid degradation of the
prototype under the desired conditions of work [12].
For this reason it was evaluated for a moment the use of wood,
but due to the high water absorption of this material it quickly
gave up the idea, though, for cost, ease of packaging and
versatility in installation process was a good option instead.
analyzed Acrylonitrile Butadiene Styreneor ABS which is the
most common plastic processes 3D printing and because of the
availability of equipment 3D printing in the research group
proceeded to the development of one of the support structures
is the piece with the major material; this to evaluate the
behavior of the material and printer at the time of making such
structures.
The result of the test with the printer revealed that the size of
the piece and the amount of material generated deformations in
the structure so it was defected from this idea [11].
Having evaluated and discarded materials such as metal, wood
and Acrylonitrile Butadiene Styrene, it was put to the use of
polymers, which according to the data sheets consulted
showing suitable values for the properties of interest in the
design.
Then, it was proposed to use Nylon (PA, polyamide 6.6) due to
its low thermal conductivity and excellent performance in
external environments, and like this, other polymers such as
polyurethane (PUR), polystyrene (PS) and high density polyethylene
( HDPE).
In this regard, A review of the structural and mechanical
properties (density) (rigidity, hardness, tensile strength) of the
proposed polymers was done; it was concluded that the high
density polyethylene (HDPE), comply fully with the
requirements demanded by the process, because tolerate
temperatures up to 120 ° C, and it has low water absorption in
moisture environments and it is chemically inert; these features
Nylon also had, but at a higher cost.
Different ideas about how the system
responsible for ensuring within the chamber specified working
conditions were raised. Taking into account that the conditions
of application in this particular case differ from those in the
laboratory essentially because geometry can be variable, a
control solution type ON-OFF was proposed, as this allows
variations in the plant which not alter significantly the
conditions of control and depend on most of the power
actuators.
Based on the set conditions, and a type on-off control it was set
out which actuators assembly would be necessary, so it was
initially thought in a system where entries were dependent on
each other; so, it was thought of two mounting:
• Heating water by using electric resistance to the desired temperature and humidify the air by an ultrasonic nebulizer.
• Heating water with electric resistance at the desired temperature and using a pump and spray system to humidify the air.
These ideas were discarded because there were no techniques known assemblies specifications and also it was not possible to work separately moisture and temperature in case of special applications, so it was necessary to separate the system into two types to work in parallel (Figure 2), which are based in ensuring uniformity and heat with the use of a fan heater and through a spray misting system challenged to humidify the chamber [12]. Fig.2.
Taking as reference points the requirements of the curing process (working temperature between 60 and 80 ° C and a moisture of 90% for periods of 24 hours), the dimensional constraints imposed in the planning stage, taking into account logistic conditions of use of the prototype, which are the characteristics of a civil work, and also knowing the type of control with the assembly, it was proceeded to select the necessary elements for the phase variator which were: Fig.3.
• The temperature system is based on the design of a caloventor which consists of an electrical resistance 110VAC 1.5A producing heat and a fan 2650 rpm (Figure 3) that drives the hot environment air, this design was the optimal based on finite element simulations that these properties determined for the actuators to be necessary to ensure uniformity and stability conditions inside the chamber Fig.4.
•System humidity The moisture system is based on the design of a spray system nebulizer which consists of water driven by an electric pump to be a normally closed hydraulic solenoid 12vdc, which controls the water to flow to a spray nozzle dig fogger with spline mounted on a coupling which allows to humidify the air.
• Control Based on a control system type on / off the Microcontroller ATmega2560 data used and through dth22 digital temperature sensor and humidity which uses a capacitive humidity sensor and a thermistor to measure the surrounding air, as it was shown by a digital signal on data pin. The only drawback of this sensor is related to that you can only obtain new data once every 2 seconds, so readings can be made will be minimal every 2 seconds, but because the system is in use for 24 hours and stabilization time is 30 minutes, sampling is in the proper range for this application. Fig.5.
The data acquisition step is performed based on a serial
communication via the microcontroller and a computer
graphical interface in Matlab (Figura6) in which proceeds to
display and monitor the behavior of the chamber.
Parallel the microcontroller depending on the reference
temperature and humidity, so on / off along with a power
conditioning integrated by optocouplers 4N35 and relays,
enables two pins that control the actuators, in the case of
system active temperature resistance and in the case of system
activates electrovalve moisture, thus, it is efficiently controlled
humidity and temperature in the chamber. Fig.6.
Aim: To determine the degree of variation in the resistance of mortar cubes of the same dosage based on steel slag and fly ash cured for 24 hours into the chamber against which were cured under laboratory conditions.
Procedure: It was done 3 trials in which the percentages of ash and slag were varied as the temperature conditions and humidity were performed as follows:
For testing 6 cubes by test were manufactured based on Colombian Technical Standard NTC220 from which half were cured in the chamber and the other half in laboratory conditions.
After the curing process it was determined resistance to the mortar cubes understanding.
The chamber has different response types depending on the
kind of test being performed; where the temperature control
system used has a damped sub behavior with a steady-state
error for the temperature of about ± 2.5 ° C and humidity to ±
2.5% RH, this is due in principle to the control operation, the
ability to respond of the caloventor to the reference and the
thermal properties and hydrophobic material [13],[14].
When the chamber is operating exclusively with humidity
control, it is obtained a transient response over-damped and
steady-state error of about ± 5% RH, because the
humidification system is slow to respond since the structure has
properties optimum sealing with the hydrophobic properties of
the material, allow to maintain stable conditions in the chamber
with minimum loss [14],[15].
The coefficients of variation of the compressive strength of
mortar cubes cured in the chamber shown in (Figure 13) are
lower compared to curing performed in the laboratory, since
the chamber has better uniformity and stability regardless of
values strength cubes or working conditions [15]-[17].
According to (Figure 12) it is confirmed that the mortar cubes, made with 50% slag and 50% fly ash, it is the ones which obtains higher values of compressive strength, compared to those made with other mortar mixtures [18]. The percentages of variation shown in (Table II) are not greater than 15%, this indicates that the variation between the results of the chamber and the laboratory are tolerable considering the industrial application to which the chamber will be put down, which will be useful for the field of civil engineering.
8. ConclusionsThe device is capable of curing with high degree of stability
and uniformity samples concrete made from slag and fly ash,
obtaining compressive strengths comparable to alkaly activated
materials cured in oven under laboratory conditions in a
continuous period of 24 hours, or comparable to Portland
cement materials with conventional curing, in continuous
periods of 24 hours.
The variation coefficients obtained when comparing the
compressive strength results between mortars cured in the
laboratory and those cured in the chamber are low, because the
fabricated chamber has better uniformity and stability in the
operation regardless of the working conditions. The assembly
of the device is easy to install and its monitoring interface
which allows a simple and efficient interaction between the
user and the device.
The development of the device is helpful for the analysis and
projects developed by the scientific community and industry as
it opens the possibility to develop a system on a real scale for
building applications and reduce transportation costs and own
costs when waste materials as replacements to Portland cement
via alkaline activation.
[1] Imbabi, M. S., Carrigan, C., & McKenna, S. (2012). Trends and developments in green cement and concrete technology. International Journal Sustainable Built Environment, 1(2), 194–216. doi: 10.1016/j.cemconres.2011.03.019.
[2] Provis, J.L., van Deventer J.S.J. Alkali-activated Materials: State-of-the-Art Report, RILEM TC 224-AAM, Springer/RILEM, Dordrecht, 2014.
[3] O. Trocónis de Rincón, Duracon Collaboration "Durability of concrete structures: DURACON, an iberoamerican Project. Preliminary results", Building and Environment, 41, (2006), p. 952-962.
[4] ACI Committee 318. Building code requirements for structural concrete (ACI 318-14) and commentary (318R-14). Michigan: American Concrete Institute; 2014.
[5] Cárdenas, J., Lizarazo, J., Aperador, W., “Comportamiento mecánico de sistemas cementantes binarios (cemento portland – ceniza volante – escoria de alto horno),” Revista Latinoamericana de Metalurgia y Materiales, vol.16, no.1, pp.78-98, Diciembre 2015.
[6]. M. Sahmaran, T. K. Erdem, I. O. Yaman "Sulfate resistance of plain and blended cements exposed to wetting-drying and heating-cooling environments", Construction and Building Materials, 21, (2007), p. 1771-1778.
[7]. B. Johannesson, P. Utgenannt "Microstructural changes caused by carbonation of cement mortar", Cem. Concr. Res., 31, (2001), p. 925-931.
[8]. E. T. Stepkowska "Simultaneous IR/TG study of calcium carbonate in two aged cement pastes", J. Therm. Anal. Cal., 84, (2006), p. 175-180.
[9]. K. Garbev, P. Stemmermann, L. Black, C. Breen, J. Yarwood, B. Gasharova "Structural features of C-S-H (I) and its carbonation in air-a Raman spectroscopic study. Part I: Fresh phases", J. Am. Ceram. Soc., 90, (2007), p.900-907.22. J. Davidovits "Geopolymers: inorganic polymeric new materials", J. Thermal Anal., 37, p. 1633-1656, (1991).
[10] H. Shin, J. Yang, Y.Yoon, D. Mitchell, “Mix design of concrete for prestressed concrete sleepers using blast furnace slag and steel fibers”, Cement and Concrete Composites, 74, 2016, p. 39-53.
[11] C. Caruana, C. Yousif, P. Bacher, S. Buhagiar, C. Grima, “Determination of thermal characteristics of standard and improved hollow concrete blocks using different measurement techniques”, Journal of Building Engineering, 13 (2017), p 336-346,
[12] S. Lim, V. Prabhu, M. Anand, L. Taylor, “Extra-terrestrial construction processes – Advancements, opportunities and challenges”, Advances in Space Research, 60, (2017), p. 1413-1429.
[13] F. Bella, D. Pugliese, L. Zolin, C. Gerbaldi, “Paper-based quasi-solid dye-sensitized solar cells”, Electrochimica Acta, 237 (2017), p. 87-93,
[14] J. Lizárraga, A. Ramírez, P. Díaz, J. Marcobal, J. Gallego, “Short-term performance appraisal of half-warm mix asphalt mixtures containing high (70%) and total RAP contents (100%): From laboratory mix design to its full-scale implementation”, Construction and Building Materials, 170 (2018), p. 433-445.
[15] A.J. Buttress, D.A. Jones, C. Dodds, G. Dimitrakis, C.J. Campbell, A. Dawson, S.W. Kingman, Understanding the scabbling of concrete using microwave energy, Cement and Concrete Research, 75 (2015), p. 75-90
[16] A. Duarte, B. Ferreira, P. Nóvoa, A. Torres, Multifunctional Material Systems: A state-of-the-art review, Composite Structures, 151 (2016), p. 3-35,
[17] M. Criado, A. Fernández-Jiménez, A. Palomo "Alkali activation of fly ash. Effect of the SiO2/Na2O ratio. Part I: FTIR study", Microp. Mesop. Mat., (2007), (disponible on line).
[18] A. Palomo, A. Fernández-Jiménez, C. López-Hombrados, J. L. Lleyda "Precast Elements Made Of Alkali-Activated Fly Ash Concrete", 8th CANMET/ACI International conference on fly ash, silica fume, slag and natural pozzolans in concrete, Las Vegas, USA, Supplementary Volume, p. 545-558, (2004).
How to cite:
C.D. Hernández-Montiel, W.A. Aperador-Chaparro, M.J. Pinzón-Cárdenas and J.W. Cárdenas-Pulido, “Design and manufacture of a prototype
scale chamber with variation of moisture and temperature for curing concretes of alkaline activation prepared from steel slag mixes and flying ashes.”,
Respuestas, vol. 23, no. 1, pp. 45 - 51, 2018.
*Doctorado en Ingeniería con énfasis en
Ingeniería de Materiales, Universidad Militar Nueva Granada, Bogotá Colombia. Correo: william.aperador@unimilitar.edu.co
**Ingeniero en Mecatrónica, Universidad Militar Nueva Granada, Bogotá Colombia.
***Maestría en Materiales y Procesos, Universidad ECCI, Bogotá Colombia.
****Ingeniero Civil, Universidad Militar Nueva Granada, Bogotá Colombia.
