Experimental study on the effect of rainfall on fresh concrete

Abstract

AL-Taifregion, in the Kingdom of Saudi Arabia (KSA), can be classified as rainy region; however, during day the weather can be changed several times means rainfall at any time. Due to the advantage of concrete too many concrete structures executed and massive quantity of concrete cast every day, some of it can subject to rainfall. An experimental program has been carried out to investigate the influences of rainfall duration on the compressive strength of fresh concrete. Concrete mixture was designated and cast in standard cubes molds 150 *150*150 mm as control compressive strength. Based on the mix quantities obtained from concrete mixture, seventy two cubes cast in three groups, each group has four subgroups with six cubes each. Three different rainfall started time from casting studied 15, 30, and 45 minutes each represented as group. Four duration of rainfall studied 10, 30, 45, and 60 minutes each represented as subgroups. Results of compressive strength test on cured specimens were used to obtain equations for prediction the influences of concrete compressive strength regarding to rainfall duration and starting time of rainfall from casting. From this research, the findings can get site decisions on whether to continue or suspend the construction based on the forecasted rainfall. On the other hand, if concrete subjected to rainfall after casting, the engineer will have an equation can be used as a guide to determine the new concrete compressive strength.

Full text

VOL. 10, NO. 16, SEPTEMBER 2015 ISSN 1819-6608
ARPN Journal of Engineering and Applied Sciences
©2006-2015 Asian Research Publishing Network (ARPN). All rights reserved.
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6773
EXPERIMENTAL STUDY ON THE EFFECT OF RAINFALL ON
FRESH CONCRETE
Ahmed S. El-amary1, 2, Badr T. Alsulami1 and Nidal M. W. AL-Bustami1
1Department of Civil Engineering, Taif University, Taif, KSA
2Department Civil Engineering, Al-Azhar University, Qena, Egypt
E-Mail: a.elamary@tu.edu.sa
ABSTRACT
AL-Taifregion, in the Kingdom of Saudi Arabia (KSA), can be classified as rainy region; however, during day the
weather can be changed several times means rainfall at any time. Due to the advantage of concrete too many concrete
structures executed and massive quantity of concrete cast every day, some of it can subject to rainfall. An experimental
program has been carried out to investigate the influences of rainfall duration on the compressive strength of fresh
concrete. Concrete mixture was designated and cast in standard cubes molds 150 *150* 150 mm as control compressive
strength. Based on the mix quantities obtained from concrete mixture, seventy two cubes cast in three groups, each group
has four subgroups with six cubes each. Three different rainfall started time from casting studied 15, 30, and 45 minutes
each represented as group. Four duration of rainfall studied 10, 30, 45, and 60 minutes each represented as subgroups.
Results of compressive strength test on cured specimens were used to obtain equations for prediction the influences of
concrete compressive strength regarding to rainfall duration and starting time of rainfall from casting. From this research,
the findings can get site decisions on whether to continue or suspend the construction based on the forecasted rainfall. On
the other hand, if concrete subjected to rainfall after casting, the engineer will have an equation can be used as a guide to
determine the new concrete compressive strength.
Keywords: fresh concrete, rainfall, concrete strength, rain duration.
1. INTRODUCTION
The most important material property in design of
concrete structures which is routinely specified and tested
by control specimens is the compressive strength of
concrete. Different countries use various kinds of
specimens in shape and size. Thus, compressive strength
of concrete specimens with similar mixtures and different
sizes and shapes are different. Most common shapes are
cylindrical and cube specimens in which cube specimen
with height 150mm and area 150x150mm is known as the
standard specimen; consequently all specimens in this
study will have the same dimensions of standard cubes.
This part will present a literature review concerning about
the research subject in the last twenty years.
It is noticed that, most of the previous study in the
above mention subject were concerned with two main
topics, Hydration and setting time and Cement paste and
bleeding; with some other different research areas. Each
will be presented separately as follow: Hydration and
setting time various empirical tests are used to study the
hardening and setting of cementitious materials. These are
sometimes alternatively described as consistency or setting
time measurements. These tests include the Vicat needle,
penetrometers of various shapes and the proctometer also
known as the Proctor needle, as stated by (Lootens and
Flatt, 2007). Some of these techniques measure the
penetration resistance (i.e. penetration force) under an
imposed speed, while others measure the penetration depth
for an imposed load. The recent developments in
ultrasound spectroscopy performed by (Subramaniam and
Wang 2010). (Schultz and Struble, 1993) allowed for the
measurement of the evolutions of both shear and bulk
elastic moduli during setting of cement paste. Based on
these new techniques, recent papers showed the existence
of a relation between shear yield stress and the empirical
setting time measurements as stated by (Nachbaur et al.
2001). These correlations show that what was defined as
initial setting time corresponds to a yield stress of the
material of the order of a couple hundred kPa. Cement
paste and bleeding; bleeding (i.e. the accumulation of
water at the surface of the paste) of potentially usable fluid
cement paste shall be neglectable. It results from the
difference in density between cement grains and water.
Bleeding, in the range of interest of industrial cementitious
materials, cannot be described as the settlement of
individual cement grains in a dilute system but rather as a
consolidation process (i.e. the upward displacement of
water through a dense network of interacting cement
grains) (Josserand et al. 2006). The interactions between
cement grains and permeability of freshly mixed cement
pastes were therefore first order parameters of a cement
paste resistance to bleeding. The bleeding phenomenon
can be slowed down by the viscous nature of the interstitial
fluid, which has to travel to the surface under the effect of
gravity. Viscosity agents can therefore be used to reduce
the amplitude of bleeding before setting as stated by
(Khayat, 1998). They were able to thicken the interstitial
water and slow down the bleeding phenomenon.

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This may reduce the practical consequences of
bleeding and make them neglectable from an industrial
point of view. (Lei and Jonathan, 2010) studied the roller-
compacted- concrete (RCC), this study based on laboratory
experiments with simulated RCC construction under
artificial rainfalls. The results detail the impact of rainfall
on RCC’s rollability, water content, vibrating compaction
value, density, and bonding strength between RCC lifts.
Reducing water content was studied as a countermeasure
to mitigate such impacts. In the experiments, the optimal
water content of 95 kg/m3 was used in preparing the
concrete mixture and the actual measured water content
was 97 kg/m3 as measured from the samples. The results
indicate that the actual water content had increased due to
rainfall; and the increase was more significant for more
intense rainfalls. If the water content below the surface
exceeds 101 kg/m3, the point was impacted by the rainfall.
At the rainfall intensities of 2.6, 5.0, and 8.0 mm/h, the
impacted depths from the surface were 100, 150, and 175
mm, respectively. The impacted depth clearly increased
with the rainfall intensity.
(Khorshidi et al. 2014) studied the effects of
magnetic water on different properties of cement paste
including fluidity, compressive strength, time of setting
and etc. For production of magnetic water, three devices
including an AFM called device(made in UAE) ,a device
marked AC(made in Germany) and finally a device was
designed and made in Concrete Laboratory of Sahand
University of Technology) had been used. The results
show that, intensity and direction of magnetic field,
velocity and time of water passing through magnetic
device, and amount and type of Colloidal particles had
direct effects on properties of magnetic water and using
such a water in making cement paste, increases its fluidity
and compressive strength up to 10%.
(Kaustav and Bishwajit, 2014) presented proposes
of numerical scheme for analysing the evolution of
moisture distribution in concrete subjected to wetting-
drying exposure caused by intermittent periods of rainfall.
The proposed paradigm was based on the stage wise
implementation of non-linear finite element (FE) analysis,
with each stage representing a distinct phase of a typical
wet-dry cycle. The associated boundary conditions had
been constituted to realize the influence of various
meteorological elements such as rain, wind, relative
humidity and temperature on the exposed concrete surface.
The reliability of the developed scheme had been
demonstrated through its application for the simulation of
experimentally recorded moisture profiles reported in
published literature. A sensitivity analysis had also been
carried out to study the influence of critical material
properties on simulated results. The proposed scheme was
vital to the service life modelling of concrete structures in
tropical climates which largely remain exposed to the
action of alternating rains. (Jiachun and Peiyu, 2013) they
measured adiabatic temperature increases of four different
concretes to understand heat emission during hydration at
early age. The temperature-matching curing schedule in
accordance with adiabatic temperature increase was
adopted to simulate the situation in real massive concrete.
The specimens under temperature-matching curing were
subjected to realistic temperature for first few days as well
as adiabatic condition. The mechanical properties
including compressive strength, splitting strength and
modulus of elasticity of concretes cured under both
temperature-matching curing and isothermal 20o C curing
were investigated. The results denoted that comparing
temperature-matching curing with isothermal 20o C curing,
the early age concretes mechanical properties were
obviously improved, but the later mechanical properties of
concretes with pure portland and containing silica fume
were decreased a little and still increased for concretes
containing fly ash and slag. On this basement they used an
equivalent age approach evaluates mechanical properties
of early age concrete in real structures, the model
parameters were defined by the compressive strength test,
and could predict the compressive strength, splitting
strength and elasticity modulus through measuring or
calculating by finite element method the concreted
temperature at early age. (Yingfang et al. 2014) studied the
behaviour of deteriorated reinforced concrete (RC) beams
attacked by various forms of simulated acid rain. An
artificial rainfall simulator was firstly designed and
evaluated. Eleven RC beams (120mm x 200mm x 1800
mm) constructed in the laboratory. Among them, one was
acting as a reference beam and the others were subjected to
three accelerated corrosion methods, including immersion,
wetting-drying, and artificial rainfall methods, to simulate
the attack of real acid rain. Acid solutions with pH levels
of 1.5 and 2.5 were considered. Next, ultrasonic, scanning
electron microscopy (SEM), dynamic, and three-point
bending tests performed to investigate the mechanical
properties of concrete and flexural behaviour of the RC
beams. It concluded that the designed artificial simulator
can be effectively used to simulate the real acid rainfall.
Both the immersion and wetting-drying methods magnify
the effects of the real acid rainfall on the RC beams.
In this study, based on the rainfall reported in
Taif, a comprehensive experimental program is conducted
to investigate the rainfall duration effects in concrete
compressive strength. The specimen divided into three
groups based on the rainfall stating time after concrete
casting (15, 30 and 45 minutes). The first group represent
rainfall started after 15 minutes from casting and the
rainfall duration was 10, 30, 45 and 60 minutes. The
second group represents rainfall started after 30 minutes
from casting and duration of rainfall as stated for group
one. The third group represents rainfall started after 45
minutes from casting and the rainfall duration as stated for
group one. Seventy eight concrete compressive strength
tests were conducted in this experimental program to
determine the compressive strength of the control cubes
and cubes subjected to rainfall. Finally the Least-Square
Method (LSM) is employed for the results of the

VOL. 10, NO. 16, SEPTEMBER 2015 ISSN 1819-6608
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6775
experimental program toobtain the rainfall duration effect
on concrete compressive strength.
1.1 Research significance
The technical and safety problems that arise when
fresh concrete subjected to rainfall show the necessity for
studying that subject in our research project.
The objectives of this study can be summarized
as:
 To get a real data about the strength of fresh concrete
if it is subjected to rainfall.
 Obtain an easy way to decide if the fresh concrete
subjected to rain water can resist the future applied
loads or not.
 Proposed an equation represent the relation between
the concrete compressive strength and duration of
rainfallbased on starting time of rainfall after casting.
1.2 Taif rainfall data
Daily meteorological data at Taif station No.
41036 was obtained from the Saudi Geological Survey.
The analysis of the rainfall data for a period of 14 years
showed that the maximum daily precipitation occurred was
of intensity of 4.3 mm/hr.
2. EXPERIMENTAL PROGRAM
2.1 Procedures
 Design a concrete mix using the available sand, gravel
and cement to determine the control compressive
strength of concrete at age 28 days.
 Cast three groups of cubes each group has four
subgroups. Each subgroup has six cubes cast using the
same designed quantities of materials per cubic meter
obtained from the design mix.
 Each group from the main three groups represents a
sum of concrete cubes subjected to rain after 15, 30
and 45 minutes from casting. The subgroups
represented by 15, 30, 45 and 60 minutes as duration
of rain. The maximum time after casting considered
45 minutes due to results of initial setting test
conducted to cement samples using Vicat needle.
2.2 Specimen design
To simulate the wooden formwork used in casting
concrete structures, cube specimens 200 x 200 x 200mm
with 12.5 mm thickness two plywood plates inserted
internally above cube base and in front of each face of the
cube as shown in Figure-1, wooden formwork simulated
and a standard cube with net dimensions 150x 150x
150mmwas performed.
Figure-1. Cubes with wooden formwork.
2.3 Materials
In order to investigate compressive strength of
concrete subjected to rainfall after casting, a concrete
mixture designed to determine control strength. Mixture
proportioning is designed to obtain average standard 28-
days compressive strength of concrete cubes
approximately 30 MPa. The mix ratios by weight of
cement were cement: sand: gravel: water 1:2.1:4.2:0.48.
Natural fine and coarse aggregates with maximum size 19
mm are used in the mixtures. Bulk specific gravities of
coarse and fine aggregates are 2.67 and 2.71 and their
water absorptions are 1.3% and 1%, respectively. Ordinary
locally-available Portland cement having a specific gravity
of 3.15 was employed in the casting of the specimens. A
laboratory concrete mixer is used for mixing the concrete
mixtures for five minutes. Standard steel cubes (150x 150
x 150 mm) specimens as the control specimens are cast
with mechanical vibration. Same producers will be
followed for all other specimens before subjected to
rainfall. After casting, the control molded specimens are
stored in the casting room for 24 hours and then are
demolded and transferred to the curing cabinet, where all
the rest of three groups specimen are subjected to rainfall
after 15, 30 and 45 minutes from casting and demolded
after 24 hours before curing.
2.4 Rainfall simulation
According to the provision of meteorology in
KSA, rainfall can be classified in different ways. One of
these ways is the rainfall intensity. In this study the rain
simulated using the rainfall simulator apparatus produced
by GUNT shown in Figure-2. In this apparatus the time of
rainfall can controller by built up controller illustrated in
Figure-3(a). The rain can be simulated by sprinklers
controlled by valves these sprinklers provided by water
lifted by pump connected to plastic water tank placed in
the bottom part of the apparatus as shown in Figure-2(b).
The discharge of each sprinkler is checked by measuring
the rainfall intensity of each using graduated beakers as

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6776
illustrated in Figure-3 (b). On the other hand, the height of
water in a certain time is measured to determine the
rainfall intensity in apparatus test area and it was
equivalent to almost 3.9 mm/hr.
Rainfall area
Rain simulation apparatus
Figure-2. Rainfall simulator apparatus.
Rain time controller
Calibration and measuring of rainfall intensity
Figure-3. Rain timer and calibration.
2.5 Test producers
A total of 78 compression strength tests
conducted to study the effect of rainfall duration on
concrete strength using calibrated universal testing
machine shown in Figures 4 and 5. The experiments were
conducted at two different variables, rainfall starting time
from casting and rainfall duration. After 28 days of curing,
load control compressive strength test based on ASTM
C39 with constant load rate of 3 kN/s is conducted for all
of the specimens and the results are given in Table-1.

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(a) Specimen under rainfall
(b) Cubes demolded and curing
Figure-4. Specimen during test and curing.
UTM Calibration test
Cube compression strength test
Figure-5. Universal testing machine, calibration and testing.
Table-1. Compressive strength test results.
Rainfall
started
Rainfall
duration (mins)
15 mins from casting
30 mins from casting
45 mins from casting
Average
compressive
strength (MPa)
% from
control
strength
Average
compressive
strength (MPa)
% from
control
strength
Average
compressive
strength (MPa)
% from
control
strength
Subgroup1
10
25.8
86%
27.0
90%
27.9
93%
Subgroup2
30
24.0
80%
25.7
86%
26.9
90%
Subgroup3
45
22.3
74%
24.0
80%
26.1
87%
Subgroup4
60
20.9
70%
22.0
73%
25.6
85%

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3. EXPERIMENT RESULTS AND ANALYSES
Figure-6. Cube failure configuration.
Average compressive strength for each subgroup
and the percentage of reduction from control strength are
given in Table-1. The results in Table-1 indicate that the
concrete compressive strength has decreased due to
rainfall; and the effect increase is more significant for
more rainfall duration. Figure-6 shows the cube failure
configuration after testing. In the experiments, the average
compressive strength obtained from concrete mixture
design was30 MPa was used as control value. Figures 7-9
illustrate the relationship between concrete compressive
strengths of standard cubes and rainfall duration started
after three different times from casting. As shown in
Figures 7-9, concrete specimen show lower compressive
strengths than control standard cube specimens. Generally,
the difference between the compressive strengths of cubes
subjected to rainfall and the control cubes significantly
affected by the starting time of rainfall from casting and its
duration. Therefore, it can be said that in rainy areas fresh
concrete compressive strength can be affected significantly
by two important factors, rainfall starting time after casting
and rainfall duration.
Compressive strength Vs rainfall duration
Curve representing relationship (LSM)
Figure-7. Concrete compressive strength and rainfall duration (rainfall started 15 mins after casting).
Compressive strength Vs rainfall duration
Curve representing relationship (LSM)
Figure-8. Concrete compressive strength and rainfall duration (rainfall started 30 mins after casting).

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Compressive strength Vs rainfall duration
Curve representing relationship (LSM)
Figure-9. Concrete compressive strength and rainfall duration (rainfall started 45 mins after casting).
In order to obtain the correlation between the
reduction in concrete compressive strengths and duration
of rainfall when it started after certain time from casting,
regression analysis consisting types of curve-fittings are
carried out on the results. Strengths are evaluated using a
least square method (LSM). R-squared value for each case
is given to indicate the accuracy of related curve-fitting as
illustrated in Figures 7-9. Therefore, equations of form

      
     
   
    
 (1)

      
     
   
    
 (2)

      
     
   
    
 (3)
can be extracted from this study to obtain the concrete
compressive strength after rainfall.
Where

 - is the concrete compressive strength affected by
rainfall; if rainfall started 15 minutes after casting (MPa).

 - is the concrete compressive strength affected by
rainfall; if rainfall started 30 minutes after casting (MPa).

 - is the concrete compressive strength affected by
rainfall; if rainfall started 45 minutes after casting (MPa).
 - is the duration of rainfall by minutes.

 - is the designed concrete compressive strength
after 28 days(MPa).
4. CONCLUSION REMARKS
An experimental simulation produced for
predicting the effect of rainfall on fresh concrete
compressive strength. Three different rainfall started time
from end of concrete casting studied. Four different
rainfall duration 10, 30, 45 and 60 minutes were studied in
each case if rainfall starting time from casting. From this
experimental work the following conclusions can be
drawn:
 The effect of rainfall starting time from fresh concrete
casting time and duration of rainfall are two important
factors have to be taken into consideration in the rainy
region.
 Fresh concrete compressive strength can be decreased
from 10% to 30% from designed compressive strength
due to rainfall effect.
 Equations for prediction the compressive strength of
fresh concrete considering the effect of rainfall
starting time and rainfall duration were achieved using
LSM method.
ACKNOWLEDGEMENTS
The authors would like to thank and highly
appreciate all kind of supports especially financial
provided by Taif University KSA; represented by Vice
Presidency for Graduate Studies and Scientific Research to
finish this research project.
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ARPN Journal of Engineering and Applied Sciences
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