CHEMICAL RESISTANCE OF HIGH PERFORMANCE

MORTARS IN WASTEWATER ENVIRONMENT

OZLEM YAVUZ-PETROWSKI, PhD.

FLORIDA ATLANTIC UNIVERSITY

JULY, 2016.

ACIDIC ENVIRONMENT - WASTEWATER

• SULFURIC ACID ATTACKS CONCRETE AND STEEL WITHIN WASTEWATER ENVIRONMENTS.

• THE EFFECT OF SULFURIC ACID ON CONCRETE AND STEEL SURFACES EXPOSED TO SEVERE WASTEWATER ENVIRONMENTS IS SERIOUS CHALLENGE FOR OUR ECOMOMY

• IN THE USA, CORROSION CAUSES SEWER INFRASTRUCTURE LOSSES ESTIMATED AT AROUND $14 BILLION PER YEAR

HOW SULFURIC ACID (H2SO4) FORMS

• H2SO4 FORMS THROUGH BACTERIALLY MEDIATED PROCESS, CALLED

“BIOGENIC SULFIDE CORROSION”

• SEWAGE ENTERS A WASTEWATER COLLECTION SYSTEM THAT CONTAINS PROTEINS INCLUDING ORGANIC SULFUR COMPOUNDS

• DISSOLVED OXYGEN IS REDUCED AS BACTERIA BEGIN TO CATABOLIZE ORGANIC MATERIAL IN SEWAGE

CHEMICAL REPRESENTATION

ORGANIC BACTERIA + SO4-2 S-2 + H2O + CO2

S-2 + 2H+ H2S

H2S (g) + 2O2 (g) H2SO4 (l)

• IN THE ABSENCE OF DISSOLVED OXYGEN AND NITRATES, SULFATES ARE REDUCED TO HYDROGEN SULFIDE

• THE HYDROGEN SULFIDE GAS IS BIOCHEMICALLY OXIDIZED IN THE PRESENCE OF MOISTURE TO FORM SULFURIC ACID.

CORROSION

• SULFURIC ACID PRODUCED BY MICROORGANISMS WILL INTERACT WITH THE SURFACE OF THE STRUCTURE MATERIAL (CONCRETE)

• SULFURIC ACID REACTS WITH THE CALCIUM HYDROXIDE IN CONCRETE (PORTLAND CEMENT) TO FORM CALCIUM SULFATE

• CONCRETE IS HARMED BY ACID ATTACK BECAUSE OF ITS ALKALINE NATURE. THE ALKALINE COMPONENTS OF THE CEMENT PASTE (CALCIUM HYDROXIDE) BREAK DOWN WITH ACID EXPOSURE.

H2SO4 + Ca(OH)2 -> CaSO4 + 2 H2O

CURRENT CEMENTITIOUS MATERIALS AND THEIR USE

• CEMENTITIOUS MATERIALS

- ‘TRADITIONAL MORTAR’, IN ITS MOST GENERAL AND BASIC FORM IS REFERRED TO AS PORTLAND CEMENT, OR TYPE ONE

- ‘HIGH PERFORMANCE’ MORTARS: THIS CATEGORY DOMINATED BY CALCIUM ALUMINATE (CA)

PREVENTION OF CORROSION OF CONCRETE

• USING MATERIALS RESISTANT TO BIOGENIC CORROSION SUCH AS EPOXY AS A BARRIER MATERIAL

• THESE ARE NOT MAGIC MATERIALS, BUT ARE SIMPLY: • NOT AS POROUS AS CONCRETE • MUCH MORE RESISTANT TO THE HIGHLY ACIDIC

ENVIRONMENTS

GOAL OF THIS STUDY:

TO TEST:

• CALCIUM ALUMINATES, AND

• NEXT GENERATION EPOXY MODIFIED MORTAR

AND TO COMPARE THEIR CHEMICAL RESISTANCE

• IN ACIDIC ENVIRONMENT (WASTEWATER)

STUDY DESIGN

• H2SO4 IS THE ACID THAT IS TO BE TESTED IN THIS STUDY • THIS IS AN ACCELERATED TEST AND WILL BE USING 31% (5. 63

M) SULFURIC ACID • CURED MATERIAL SAMPLES WILL BE IMMERSED IN H2SO4

• EACH SAMPLE WILL START OUT AT APPROXIMATELY THE SAME WEIGHT AND SIZE

• SAMPLES WILL BE WEIGHED WEEKLY TO DETERMINE RESPECTIVE WEIGHT LOSS

• WEEKLY OBSERVATIONS WILL BE CARRIED OUT 7 CONSECUTIVE WEEKS

INITIAL MATERIAL SAMPLES

Sample 1 (calcium aluminate mortar, 987.6 g)

Sample 2 (epoxy modified mortar, 994.9 g)

Sample 3 (100% pure fused calcium aluminate, 981.1g)

AFTER 1 WEEK OF EXPOSURE TO H2SO4 Sample 1 (calcium aluminate mortar, 692 g)

Sample 2 (epoxy modified mortar, 1050.2 g)

Sample 3 (100% pure fused calcium aluminate, 745.9)

Samples shown

together

AFTER 2 WEEKS OF EXPOSURE TO H2SO4

Sample 1 (calcium aluminate mortar, 534 g)

Sample 2 (epoxy modified mortar, 1052.5 g)

Sample 3 (100% pure fused calcium aluminate, 617 g)

Sample 1 (calcium aluminate mortar, 433.6g)

Sample 2 (epoxy modified mortar, 1059.1 g)

Sample 3 (%100 pure fused calcium aluminate, 531.0g)

AFTER 3 WEEKS OF EXPOSURE TO H2SO4

Sample 1 (calcium aluminate mortar, 365.1g)

Sample 2 (epoxy modified mortar, 1054.1g)

Sample 3 (100% pure fused calcium aluminate, 474.7g)

AFTER 4 WEEKS OF EXPOSURE TO H2SO4

Sample 1 (calcium aluminate mortar, 315.6 g)

Sample 2 (epoxy modified mortar, 1064.5g)

Sample 3 (100% pure fused calcium aluminate, 432 g)

AFTER 5 WEEKS OF EXPOSURE TO H2SO4

Sample 1 (calcium aluminate mortar, 275.7 g)

Sample 2 (epoxy modified mortar, 1063.6 g)

Sample 3 (100% pure fused calcium aluminate, 393.0 g)

AFTER 6 WEEKS OF EXPOSURE TO H2SO4

Sample 1 (calcium aluminate mortar, 244.8g)

Sample 3 (100 pure fused calcium aluminate, 361.7g)

AFTER 7 WEEKS OF EXPOSURE TO H2SO4

Sample 2 (epoxy modified mortar, 992.3 g)* *After removing loose external scale – simulating power wash

WEIGHT LOSS STUDIES IN 31% H2SO4

0

200

400

600

800

1000

1200

Initial Week 1 Week 2 Week 3 Week 4 Week 5 Week 6 Week 7

CaAluminate Mortar

Epoxy Modifed Mortar

100%FusedCaAluminateMortar

Number of Weeks

Wei

ght,

g

Sample 1 (calcium aluminate mortar: PH 6-7)

Sample 3 (100 pure fused calcium aluminate: PH 7)

AFTER 7 WEEKS OF EXPOSURE TO H2SO4 PH LEVELS OF CORE CENTERS:

Sample 2 (epoxy modified mortar: PH 13)

SUMMARY OF OBSERVATIONS • 100 % PURE FUSED CALCIUM ALUMINATE MORTAR HAS BETTER

PERFORMANCE COMPARE TO CALCIUM ALUMINATE MORTAR BUT STILL RESULTS WAY BEHIND OF EPOXY SAMPLE

• EPOXY MODIFIED MORTAR SAMPLE SHOWED BEST PERFORMANCE IN 31 % H2SO4

• WEIGHT LOSS OF: I. CALCIUM ALUMINATE MORTAR IS 75%, II. 100 % FUSED CALCIUM ALUMINATE IS 63% III. EPOXY MODIFIED MORTAR 0.3%

AFTER 7 WEEKS WORTH OF EXPOSURE TO H2SO4

SUMMARY OF OBSERVATIONS • PH LEVELS:

• LEVELS OF 7 NEUTRAL. THE HIGHER THE LEVEL THE STRONGER THE SAMPLE REMAINS AND CONTINUE TO GET.

• LEVELS OF 10 OR LOWER HAVE BEEN OBSERVED TO AFFECT THE CORROSION OF ANY EMBEDDED STEEL REBAR WITHIN CONCRETE.

• OBSERVED LEVELS AFTER 7 WEEKS: I. CALCIUM ALUMINATE MORTAR PH 6-7 II. 100 % FUSED CALCIUM ALUMINATE PH 6-7 III. EPOXY MODIFIED MORTAR PH 13.

AFTER 7 WEEKS WORTH OF EXPOSURE TO H2SO4