









































Abstract: Marine concrete can be especially susceptible to chemical and physical deterioration, including corrosion 
of the reinforcement steel.  For this reason, pozzolans such as fly ash, blast furnace slag, and silica fume, are 
commonly used to reduce corrosion in concrete subjected to marine environments by decreasing the permeability 
of the concrete matrix. The permeability of a concrete matrix is commonly used to indicate the susceptibility of a 
concrete to the corrosion of the steel reinforcement due to its effects on initial corrosion and subsequent corrosion. 
The water/cementitious materials (w/cm) ratio, binder type, curing conditions, and compaction factors can impact 
the level of permeability.  A lower w/cm ratio can reduce the permeability, as does the addition of pozzolans. Ground 
glass is currently under intense scrutiny for its potential as a pozzolan in portland cement concrete, as it differs from 
other pozzolans due to its high alkali content. This research considers the potential for ground glass use as a pozzolan 
in marine concrete applications. 

Aisthesis      Volume 9,  201823

Glass Pozzolans in Marine Concrete
by Ashley Murr

Marine Concrete
Concrete literally forms the foundations of our 

societies and supports our civilizations.  In 2017, 
the world produced approximately 23 billion tons 
of concrete from 4.1 billion tons of cement (USGS, 
2017).  While most of the visible concrete is used 
in buildings and roadways, there are hidden tons 
of concrete beneath the ground and in the water.  
Any concrete that is in contact with water, almost 
exclusively in reference to seawater or the influence 
of seawater, is known as marine concrete (Alexander 
& Nganga, 2016).  Such concrete is used for structures 
in marine environments.

Harsh mechanical and chemical wear warrants 
strict expectations to ensure that concrete in marine 
environments performs safely for its lifetime.  In 
the United States, the American Concrete Institute 
(ACI), provides codes for concrete used in marine 
environments which prescribe safety and durability 
standards.  Classifications defined by ACI detail 
specific exposure zones and subsequent composition 
and strength requirements for marine concrete.  In 
general, marine concrete requires higher strength 
and lower w/cm ratios compared to concrete for 
ordinary purposes (ACI 318, 2014).
    
Deleterious Conditions

Specific threats posed to marine concrete 
include freeze thaw cycles, tidal erosion, and most 
notably, chloride penetration.  These factors directly 

influence the design criteria for the concrete.  To 
segregate the severity of these threats, three marine 
exposure are defined.

These distinct marine exposure zones affect 
the rate at which the concrete will erode and 
the mechanisms for chemical transport and 
deterioration (Otenio 2015; Jakobsen, et. al. 2016).   
There are three zones which are considered: 1) the 
atmospheric zone, 2) the splash zone, and 3) the 
submerged zone.   Figure 1 illustrates the marine 
environment zones with the corresponding corrosion 
zones. Each zone exposes the concrete to unique 
conditions.  The atmospheric zone raises concerns 
primarily regarding carbonation due to humidity 
and temperature (Santhanam & Otieno 2016). 

Figure 1. Marine environment zones and subsequent corrosion 
zones. Based on information from “1 - Introduction: Importance 
of marine concrete structures and durability design,” by M. G. 
Alexander and G. Nganga, in  M. G. Alexander (Ed.), Marine 
Concrete Structures (p. 1-13), 2016, Woodhead Publishing.



Glass Pozzolans in Marine Concrete

Aisthesis      Volume 9,  201824

Concrete exposed to the splash and tidal zones 
encounter a vast range of physical mechanisms 
including abrasion, erosion, diffusion, sorption, wick 
action, and permeation which also worsen chemical 
mechanisms.  Notably, the physical mechanisms 
significantly increase the transport of ions which 
cause chemical deterioration and corrosion.  These 
zones are generally recognized as exhibiting the 
worst conditions (Santhanam & Otieno, 2016).

Most of the concern for submerged concrete 
is the permeation of chloride ions which corrode 
the reinforcing steel.  Other ion absorption and 
sulfate attack are also of major concern in this zone. 
Supplementary cementitious materials combat the 
potential risks associated with this region and, to a 
lesser extent, the previous regions.  

Specifications
The specifications regarding marine concrete 

are generally prescriptive-based but are increasingly 
becoming performance-based.  In the United States, 
ACI 318 prescribes standards for water content, 
water/cementitious material ratios, and strength.  
Marine concrete typically must meet a w/cm ratio of 
0.4 and a minimum 28-day strength of 5000 psi (ACI 
318, 2014; Suprenant, 1991).  Additional guidelines 
for marine concrete include CIRIA (Dupray et. al., 
2010), PIANC (2015), and BS 6349-1-4 (2013).  These 
guidelines offer recommendations for the materials 
and proportions used, techniques, and testing of the 
concrete. 

Pozzolans
Although portland cement remains the binder 

of choice for the vast majority of concrete projects, 
pozzolans modify and enhance properties of portland 
cement concrete when added as supplementary 
cementitious materials (SCMs). Fly ash, slag, silica 
fume, metakaolin, and glass are among the common 
pozzolans.  A pozzolan is a silica and/or alumina 
rich material that by itself possesses no cementitious 
properties but, when finely divided and reacted with 
water and calcium hydroxide, produces a binder with 
cementitious properties (ACI Concrete Terminology, 
2017). Pozzolans contribute different properties 
based on physical and chemical characteristics.  
When added to marine concrete, pozzolans combat 
the deleterious conditions resulting from the harsh 
environments.

Pozzolans can be classified as natural or artificial 
depending on their source or origin.  Current 
research is widely investigating the use of pozzolans 
in portland cement replacements, and a number 
of pozzolans are successfully employed in the field 
(Walker, et al., 2010; Tadayon, et al., 2016). 

Use in Marine Concrete
Compressive strength and chloride ion resistivity 

are crucially important properties in marine concrete.  
The compressive strength indicates safety and varies 
by purpose, as specified by ACI.  However, in the 
splash and submerged zones, the design standards 
revolve around the permeability of the concrete, as 
it indicates the resistivity to chloride ion penetration 
(Santhanam & Otieno, 2016; Allen & Moore, 2016). 
The penetration of chloride ions has the potential to 
corrode reinforcing rebar, compromising structural 
integrity (Kwon et al., 2017; Otieno, 2014).

Pozzolans may decrease the deleterious effects 
of seawater on concrete because of their chemical 
composition and microstructure.  Fly ash, blast 
furnace slag, and silica fume are commonly used.  
One characteristic of successful pozzolans is fine 
particle size, which reduces the gaps between binder 
products and aggregates in addition to reducing the 
interstitial transition zone (ITZ), therefore decreasing 
weak spots and permeability.  Additionally, higher 
alumina content increases reactions with the chloride 
ions.  The chloride is then bound within the concrete 
matrix and does not reach the steel, thereby reducing 
corrosion.  These pozzolans can also reduce the w/
cm ratio which reduces permeability and absorption 
to reduce ions that enter the concrete matrix (Moffatt 
et al., 2017; Saha, 2017; Kouloumbi et al., 1994; Nath 
et al., 2018; Thomas, 1996)

Glass as a Pozzolan
Pozzolans are silica rich materials that exhibit 

cementitious properties when reacted with calcium 
hydroxide (ASTM C595, 2017). They can replace a 
portion of the portland cement as supplementary 
cementitious materials (SCMs).  Historically, SCMs 
were added to enhance the properties of cement, 
where, for much of the twentieth century, fly ash and 
slag were used to increase flow and other properties.  
Today, however, natural pozzolans, such as waste 
glass, attract most of the research efforts (Shi & 
Zheng, 2007; Islam et al., 2016; Du & Tan, 2015; 
Shayan, 2005; Kamali & Ghahremaninezhad, 2016).



Glass Pozzolans in Marine Concrete

Aisthesis      Volume 9,  201825

Glass Background
Bottles, windows, and electronics compose the 

vast majority of glass products with the largest sector 
being bottles, or what is more formally considered 
container glass.  Container glass is also considered 
soda lime glass because of its composition and 
is typically designated as a nondurable good by 
the US Environmental Protection Agency (EPA).  
Approximately 11.5 million tons of waste glass 
is generated in the US each year.  In 2014, nearly 
3 million tons of that glass was recycled (U.S. 
Environmental Protection Agency, 2016). Bottle 
drops, curbside pick-ups, commingled municipal 
recycling facilities, and commercial waste transports 
all contribute to the pool of recycled glass, with 
each recycling facility varying in waste stream 
characteristics and end product.  Generally, however, 
recycled glass is used to produce new glass.  Once 
at the recycling facility, the glass is usually sorted 
by color for new glass products.  Of the 3 million 
tons recycled, an additional 1.5 million tons fail to 
meet strict color or particle size standards, becoming 
destined instead for the landfill.  These 1.5 million 
tons could have great potential and would not only 
improve the sustainability of the concrete industry, 
but would also divert a valuable resource from 
landfills.

Industry standards accept that for every ton 
of portland cement produced, 0.88 tons of carbon 
dioxide are produced and subsequently released into 
the atmosphere.  In total, this amounts to between 5% 
and 8% of global carbon dioxide emissions each year.  
Using a process similar to the EPA’s WARM Version 
13 Model for the greenhouse gas emissions for fly 
ash, an estimation for greenhouse gas emissions for 
ground glass can be performed.  Unlike portland 
cement, glass itself produces no excess carbon 
dioxide.  Instead, the only source of greenhouse 
gas emissions originate from the energy required to 
grind the glass, which produces approximately 10.2 
lbs of carbon dioxide for every ton of concrete.  In 
other words, the ratio of carbon dioxide to concrete 
production is 0.005.  Following the calculations, if 
a typical glass replacement rate of 20% is used, the 
resulting ton per ton carbon dioxide emissions 
decreases from 0.88 to a ratio of 0.705, yielding a 
total a reduction rate of 20%. 

Structure and Composition
Glass is considered a pozzolan replacement 

due to its high silica content and amorphous, or 
noncrystalline, structure.  Its basic molecular 
composition and structure lend to favorable 
properties for portland cement replacement.  
Additionally, the availability of waste glass suggests 
a reliable source and profitable market.  When 
considering the market availability, economic 
viability, smaller carbon footprint, and both physical 
and chemical properties, evidence supports the 
investigation of using waste glass as a pozzolanic 
replacement in cement.

Compared to other pozzolans such as fly ash and 
slag, glass has a lower calcium content and higher 
silica content (see Figure 2).  

The high silica and alumina of ground glass has been 
suggested to reduce the chloride ion penetration in 
portland cement concrete (Omran & Tagnit-Hamou, 
2015; Peyvandi et al., 2013; Du & Tan, 2017). As 
hydration occurs, silica and alumina become 
available in the concrete matrix.  These available silica 
and alumina cations plausibly attract the negatively 
charged chloride ions, creating bonds which prevent 
the chloride ions from penetrating further into the 
matrix and corroding the reinforcing steel.

Since glass lacks calcium in comparison to 
portland cement and other pozzolans, concerns 
regarding compressive strength have historically 

Figure 2. Ternary diagram comparison (Schlosser, 2017).



Glass Pozzolans in Marine Concrete

Aisthesis      Volume 9,  201826

been raised.  However, this concern has been 
addressed and resolved through numerous studies 
on pozzolans.  Because the pozzolanic reaction 
is slower than typical portland cement reactions, 
concretes using pozzolans may show lower early 
strength but eventually show higher late strengths.  
A multitude of studies support this trend and note 
that to attain adequate strength in portland cement 
concrete mixes, replacement rates should be around 
20% by mass (Du et al., 2015; Shayan & Xu, 2005; 
Kamali et al., 2016; Knmiri et al., 2012; Aliabdo et 
al., 2016).
  
Current Use in Concrete

Although not yet widely used in the industry as 
a portland cement replacement, glass is attracting 
more investigative and implementation efforts.  The 
ACI technical subcommittee on natural pozzolans 
continues to synthesize research efforts into a 
comprehensive document available for the industry.  
Current investigation regards the use of glass 
pozzolans for inland use and typical construction.  

Research Gaps 
While an abundance of research exists for glass 

pozzolan properties in standard concrete, no research 
exists for its properties in regard to its performance 
in marine concrete.  Specifically, data regarding 
chloride resistivity is lacking.  Future research should 
investigate the feasibility of using glass in marine 
concrete based on its chloride resistivity. These 
efforts would provide additional information on the 
chemical properties of glass pozzolans in portland 
cement concrete.   

Summary
Marine concrete is subject to unique 

environments classified as marine exposure zones.  
Detailed specifications outline the performance for 
marine concretes, and pozzolans have successfully 
been used to meet these specifications.  Pozzolans 
replace portions of portland cement in concrete, 
reducing the concrete’s carbon footprint and also 
enhancing concrete properties.

Glass is a pozzolan under abundant investigation 
for its potential use in concrete.  However, no research 
exists investigating its use in marine concrete.  Data 
on its chloride resistivity will indicate its feasibility 
for use in marine concrete.

References
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