And Other Stuff…
ENGR 45, SRJC
GianCarlo Santa Cruz
HempCrete and Concrete
Objective: Our project was to determine the
compressive strength of HempCrete
compared to other aggregate materials used
•Concrete and its properties.
•Hemp and its qualities.
•Why Hemp is a viable and used as an alternative
•Testing it against traditional methods.
• Concrete is a composite material consisting of cement
(commonly Portland Cement), aggregate (rocks/sand), water,
and chemical admixtures
• Concrete solidifies and hardens through the chemical process
of hydration, where the water reacts with the cement, binding
the other components together
• Has very high compressive
strength, but low tensile strength
• All concrete structures will crack
to some extent, due to shrinkage
• Very low coefficient of thermal expansion, shrinks
as it matures
• Its elasticity is relatively constant at low stress levels
but it starts decreasing at higher stress levels as
concrete increases overall
tensile strength by adding
steel reinforcements bars,
steel fibers, glass fibers or
plastic fibers to carry
History of Concrete
• The Egyptians used lime and gypsum cement,
possibly in the pyramids
• Widespread use of Roman concrete, made of
quicklime and volcanic rock
• Revolutionized building by allowing larger
and more complex structures
• Absence of steel reinforcement limited tensile
• Today concrete is used more than any other
man-made material in the world
What is the Most Consumed Substance on the Planet?
Concrete, produced at an estimated rate of 7 billion
cubic yards per year, is the second most widely
consumed substance on Earth, after Water.
The United States uses 891 lbs. of cement per person each year.
California uses 860 lbs and Nevada uses 2,170 lbs. per person
each year! Source: US Census 2000 & USGS Mineral Survey.
Pop Quiz: For a bag of M&M’s
What is the largest single public works project in the history of the
United States, containing 3.25 million cubic yards of concrete,
which is enough to pave a two-lane highway from San Francisco
to New York.
Theory Behind HempCrete
• The mixture of sand, cement, and hemp to create
an alternative form of concrete.
• Two main types of HempCrete:
-Hemp bast fiber-greater structural strength
-Pith/hurds-less predominant in textiles
• Hemp fiber increases tensile and compressive
strengths, reduces shrinkage and cracking, similar
to rebar or fiberglass.
• Hemp hurds are also uncommonly rich in silica.
• When mixed with lime, hemp hurds change from
a organic product to a mineral. As a mineral state
it is often referred to as hemp stone.
• Several hundred houses have been built in Europe
using this material.
•Buds grown for
not contain structural
What We Look For
reveals plant sex and
for obtaining seeds,
presence of this plant
will make undesired
•This is where we
obtain textile hemp.
•Longer bast used for structural
•Outer bark and inner hurds,
shorter and courser in nature,
not usually used for textiles.
•The desired bast can be obtained
by lightly shaving the bark away,
while shaving down to the core
without penetrating the interior.
1. Plant Description
Hemp (Cannabis sativa L.) is an annual herbaceous plant with
a slender stem, ranging in height from 4 to 15 feet and a
diameter from 1/4" to 3/4". The innermost layer is the pith,
surrounded by woody material known as hurds.
2. Soil and Soil Preparation Soils
Industrial hemp can be grown on a wide variety of soil types.
Hemp prefers a sufficiently deep, well-aerated soil with a
pH of 6 or greater
To achieve an optimum hemp yield,
twice as much nutrient must be
available to the crop as will
finally be removed from the soil
at harvest. A hemp field produces
a very large bulk of vegetative
material in a short vegetative
period. The nitrogen uptake is
most intensive the first 6 to 8
weeks, while potassium and in
particular phosphorous are needed
more during flowering and seed
formation. Industrial hemp
requires 105 to 130 lbs./acre (120
to 150 kg./ha) nitrogen, 45 to 70
lbs./acre (50 to 80 kg/ha)
phosphate and 52 to 70 lbs./acre
(60 to 80 kg/ha) potash.
(vegetation and flowering)
4. Growing Conditions
Hemp prefers a mild climate, humid atmosphere, and a rainfall of at
least 25-30 inches per year. Good soil moisture is required for seed
germination and until the young plants are well established.
• There are two types of industrial hemp based on their use.
• fiber cultivars - with long stalks and little branching; (shown to the
• seed cultivars - with shorter stalks, larger seed heads and may have
numerous branches (seed contains 30 - 35% oil). (shown to the left)
Why It is a Viable Alternative
• Renewable resource.
• Applied across many
• Readily grown.
• “Industrial hemp” that
were bred over time
for industrial uses
such as fuel, fiber,
paper, seed, food, oil,
• Recreational Purposes
Current Global Hemp Usage
• Countries where hemp is grown as an agricultural crop,
the police have experienced the criminal burdens that
other countries face. In fact, there are over 30 powerful
nations on the planet currently growing industrial
– These include Canada, Australia, England, France,
Germany, Austria, Spain, Russia, and China.
• These previous successes explain why legislation is
pending to deregulate industrial hemp and/or allow
scientific study by state universities is pending or
passed in over 20 states:
– Bills Passed: ND, HI, MN, IL, MD -- Resolutions Passed:
AK, CA, KY, MT, VA, VT
Legislation In Process: SD, IA, ME, NH, NM, OR, TN -Voter Initiatives: AK, CO, MI
Real World Application
• Inspirational HempCrete
• Buildings account for thirty-eight percent of the CO2 emissions in the U.S.,
according to the U.S. Green Building Council, and demand for carbon
neutral and/or zero footprint buildings is at an all-time high. Now there is a
new building material that is not just carbon neutral, but is actually carbon
negative. Developed by U.K.-based Lhoist Group, Tradical® Hemcrete® is
a bio-composite, thermal walling material made from hemp, lime and
water. What makes it carbon negative? There is more CO2 locked-up in the
process of growing and harvesting of the hemp than is released in the
production of the lime binder. Of course the equation is more complicated
than that, but Hemcrete® is still an amazing new technology that could
Real World Application
• Good looking, environmentally friendly and
100% recyclable, Hemcrete® is as versatile
as it is sustainable. It can be used in a mindboggling array of applications from roof
insulation to wall construction to flooring.
Hemcrete® is waterproof, fireproof, insulates
well, does not rot [when used above ground]
and is completely recyclable. In fact, the
manufacturers say that demolished
Hemcrete® walls can actually be used as
• Obtaining hemp
• Extraction of hemp
• Making of the base
• Determining the Ratio of
mortar to aggregate
• Construction of the test
• Testing the samples
Traditional Means of Obtaining Bast
•Bacterial Removal , through retting, of
outer bark and inner hurds.
•Done by retting using bacteria
•Retting through chemicals.
•Dew retting: leaving cut stalks in
humid fields; this allows the
elements to decompose the outer
bark and inner hurds.
•New techniques use ultrasounds and
•After this process, the remaining bast
may be separated directly and used in
How We Attempted to Replicate Retting
• Since we lack traditional
means for retting, we used
knives to attain the acquired
layer, simulating the process.
•By shaving off the bark, and
lightly whittling the hemp, we
could isolate the bast fibers,
without penetrating the core.
•What We Want
•What We Don’t Want
Extraction of Hemp
Nerds w/ Knives
Determining the Ratio of Water To Mixture
• Bag says 4 qts for every 60 lbs of mortar, let’s
make it friendly tho:
• 60 lbs mortar = 27.2 kg mortar
• Mass of 1 cup of mortar = 383.2 g
• 1 quart = 4 cups
• Ratio cups/grams = 5.88 x10-4
• Water/Cup Mortar = .225 water/cup
• For simplicity, we made an excess of concrete
for the form(s) using 10 cups of mortar and 2.5
cups of water to ensure adequate saturation.
Determining the Volumetric Ratio Between
Unmixed Mortar and Hardened Mortar
•In order to ascertain a specific volumetric ratio between the
mortar and the aggregate, we first had to obtain a ratio in
between unmixed mortar and its final volume when cured.
•After using one cup of
mortar and the
we constructed a test
•After curing we placed the test piece into a graduated container
and measured the water displacement, this was 215 ml which is
equivalent to its volume of 215 cm3.
•We also calculated the volume mathematically by measuring the
height (4.572 cm) and radius (3.81 cm) and inputting them into
π(r)2h which equals 208.5 cm3.
•From this we use the average volume of 211.75 cm3.
Determining Ratio of Aggregates
•We first created an insulated piston
using duct tape and a can.
•Without aggregate, we inserted the can
into the form and marked off the initial.
•We then packed aggregate inside the
form until the height difference was 4.6
cm-packing was necessary to ensure
adequate volumetric distribution.
•Using the 1 part aggregate, we added it
to 10 parts mortar.
Cut Metal Shavings
Making the Forms
Using a 4-in
diameter pipe and
lots of vegetable
oil… It gets stuck
By using postal
tubes, we cut
that can be pulled
off the samples,
rather than trying
to pull the sample
from the form.
Mixing the Samples
Curing and Removal of Samples
•Cardboard shipping tubes proved far
easier to remove than plastic tube.
•Just peel the cardboard away and pull
•This also negates the risk for any
further knife injuries!
In addition to testing HempCrete, we
also tested the following mixes:
-Mortar w/ Steel Wool Aggregate
-Mortar w/ Fiberglass Aggregate
-Standard Control Mortar Mix
-Standard Concrete Mix
-Different Ratios of Mortar &
Testing the Samples
Compressive Strength of Concrete
Max Compressive Strength (psi)
Max Compressive Strength (psi)
Volume Percent Mortar
The “What” Moment
• At one point in our experiment, we did actually
create a sample that maxed out the 250,000 lb
• By crushing random things, we found that a
sample stuck in a plastic tube was capable of
withstanding the 125 ton force!
•By far, the combination of a soft and
hard medium, although incidentally,
provided the best results.
•We can also conclude that out of all
the aggregate, the metal shavings were
the strongest, which is understandable
when we consider its applications in
industrial and commercial
•Despite hemp’s poor performance, we observed that it’s
max load was similar to that of fiber glass.
• Although hemp does not increase structural
strength by what we had assumed, it does,
however, exhibit structural properties similar to
that of fiber glass.
– This is important because we now know that Hemp,
being carbon negative and a renewable resource, is a
viable alternative aggregate, while maintaining some
• Our experiments also showed how a soft medium
combined with a hard medium, will have a
significant increase in structural strength, thus
providing the next ENGR 45 classes with future
Special thanks to all the California growers who made this
Only two humans were harmed in the making of this